The role of the psycho-oncologist in the psychological support of the families of cancer patients during the course of chemotherapy is one of the important parts of comprehensive cancer care, because chemotherapy not only causes physical changes in the patient, but also affects the psychological and emotional atmosphere of the family, and family members may face changes in family roles and responsibilities at the same time with concerns about the effectiveness of treatment, drug complications, future of the disease, treatment costs, and the possibility of recurrence. From the perspective of psycho-oncology, the family is considered a part of the treatment process and the mental health of its members can affect the quality of patient support, communication with the treatment team, and adaptation to the conditions of the disease. The theoretical foundations of these interventions are based on the bio-psychosocial model, family-centered approach, stress and coping theory, and the concept of self-efficacy, and the family's reaction is the result of the interaction between the patient's physical condition, cognitive perceptions, emotions, supportive resources, and social conditions. The initiation of chemotherapy may be associated with feelings of shock, fear, and uncertainty for the family, and the observation of complications such as nausea, fatigue, weakness, change in appetite, hair loss, and changes in the patient's appearance can increase the distress of family members. In the first step, the psycho-oncologist should assess the level of psychological distress of family members and identify factors such as anxiety, depression, sleep disturbances, feelings of helplessness, fear of death, economic worries, and caregiver pressure. This assessment should be done individually, as the reactions of spouses, parents, children, or other caregivers may differ from one another. One of the most important tasks of a psycho-oncologist is to provide psychological education about the family's natural responses to cancer and chemotherapy so that family members can distinguish between a normal response to stress and severe and disruptive distress. Proper awareness can prevent the catastrophic interpretation of many changes in the course of treatment, although medical information about complications and the treatment process should be provided and coordinated by the medical team. In the cognitive-behavioral approach, the psycho-oncologist helps family members identify automatic thoughts and negative predictions; for example, thinking that any physical complication is a sign of treatment failure can cause severe anxiety and disrupt the functioning of the family. Cognitive restructuring helps the family distinguish between probability and certainty and process medical information without excessive interpretation. Another important component is to strengthen the skills of the family It is a coping so that the family can use adaptive strategies in the face of the pressures of a period of chemotherapy. Daily planning, prioritizing tasks, dividing responsibilities, using social support, and allocating time for rest can prevent the accumulation of stress. The psycho-oncologist can also teach family caregivers that supporting the patient does not mean doing everything for him, and that the patient's independence and abilities should be maintained as much as possible. In many families, the fear of harm leads to excessive care, limitation of activities, or constant control of physical posture, and these behaviors may increase feelings of dependence and anxiety over time. Teaching effective patient-family communication is another use of intervention, as family members sometimes do not talk about their fears and concerns to protect the patient, resulting in silence and misunderstanding. The psycho-oncologist can teach the skill of active listening, expressing feelings, asking for help, and talking without blame so that family members can voice their concerns in a healthy way. In families where there is disagreement about treatment, family meetings can help clarify concerns and reduce conflict, provided that the patient's preferences and independence are respected. Another important task of a psycho-oncologist is to support children and adolescents in the family, as they may interpret parental behavioral changes, frequent absences from home, or changes in the patient's physical condition in different ways. Training parents to talk to the child's age and create a sense of security can prevent the formation of misconceptions and severe anxiety. Paying attention to the needs of the patient's spouse is also important, as the spouse may simultaneously play the role of an emotional partner, caregiver, treatment coordinator, and responsible for the family's financial affairs, and as a result, face double pressure. Caregiver support includes self-care training, time management, recognizing signs of burnout, and using a support network. The psycho-oncologist should remind the family that paying attention to caregiver mental health is part of caring for the patient and should not be seen as selfishness or shortcomings. Relaxation, breathing, mindfulness, and emotion regulation techniques can also be used to reduce psychological arousal in situations such as waiting for test results or visiting a chemotherapy center. In some families, the fear of the outcome of treatment and the recurrence of the disease is so intense that all family life is organized around cancer; psycho-oncological interventions can help members maintain parts of their normal lives, social relationships, and meaningful activities while caring for the patient. Establishing a support network of extended family, friends, support groups, and specialized services can also reduce feelings of loneliness and helplessness. Working with the oncology team, the psycho-oncologist can play the role of a psychological communication mediator, helping the family to ask questions on a regular basis, receive better treatment information, and separate their emotional concerns from medical issues. However, this role does not mean interpreting test results or providing medical advice, and medical decisions should be made by qualified members of the treatment team. One of the important uses of psychological support is to prepare the family for possible changes in the course of chemotherapy so that members can better manage their reactions and the patient's reactions and seek help in a timely manner in the event of severe distress. Continuous monitoring of the family's mental state is also essential, as distress may be moderate at the beginning of treatment but may worsen as the course of treatment is prolonged, complications increase, or the condition changes. The major challenge in this area is the family's excessive focus on the patient and the neglect of their own psychological needs; some caregivers may feel that they do not have the opportunity or the right to address their personal problems. Economic pressure, frequent commutes, being away from home, responsibility for caring for children, and impaired work activities can also make psychological support difficult. Cultural differences and family beliefs about cancer and chemotherapy also affect how they receive information and use psychological services. Some families may see a visit to a psycho-oncologist as a sign of a serious mental health problem and avoid getting help, so introducing services as a normal part of comprehensive cancer care can increase participation. One of the limitations of psycho-oncological interventions is that it is not possible to address all sources of family stress through psychological intervention; the severity of the disease, the complications of chemotherapy, economic conditions, social support, and the quality of health services are important factors that are outside the direct control of the psycho-oncologist. Also, a single intervention program cannot be suitable for all families, and it is necessary to adjust the intensity and type of support based on the family structure, stage of the disease, age of the patient, level of dependence, and psychological needs of the members. In families where there is severe anxiety or depression, serious dysfunction, or harmful thoughts, specialized evaluation and appropriate referral are necessary. Overall, the role of the psycho-oncologist in the course of chemotherapy is to create a safe space for the expression of emotions, increase psychological awareness, strengthen coping skills, improve family communication, prevent caregiver burnout, and help maintain a balance in family life. This support will be most effective when it begins from the beginning of treatment, continues throughout the course of chemotherapy, and is adjusted to the changing needs of the patient and the family. It is not the complete elimination of fear and worry, but rather the empowerment of the family to face treatment realistically and flexibly, maintain the mental health of the members, and provide appropriate emotional and practical support for the patient on the path to cancer treatment.