Psycho-oncology examines the psychological, emotional, and social dimensions of cancer and its consequences during and after treatment. One of the most important challenges for cancer survivors is the fear of recurrence, which can persist even after the successful completion of treatment, affecting quality of life, social relationships, and mental health. Fear of recurrence is usually associated with anxiety about recurrence, sensitivity to physical symptoms, anxiety during follow-up tests, and mental preoccupation with the future. The severity of this fear varies from person to person, and factors such as the type and stage of cancer, treatment experience, social support, history of anxiety, and the way the person deals with emotions play a role. In the meantime, emotion regulation is one of the important mechanisms for modulating psychological reactions to the fear of relapse. Emotion regulation refers to a person's ability to identify, accept, manage, and moderate unpleasant emotions and can help survivors react more appropriately to thoughts and feelings related to the illness without suppressing or exacerbating fear. People who use adaptive strategies such as acceptance, cognitive restructuring, problem-solving, mindful attention, and distress tolerance tend to have a greater capacity to manage relapse-related concerns; in contrast, rumination, catastrophizing, emotional avoidance, and persistent repression of emotions can perpetuate anxiety and increase mental preoccupation with the likelihood of relapse. Research evidence in psycho-oncology emphasizes the link between fear of relapse, anxiety, depression, rumination, and decreased quality of life, and suggests that psychological interventions can play a role in managing this concern. In clinical practice, the psycho-oncologist can first assess the severity of a person's fear of relapse and emotion regulation techniques, and then use cognitive-behavioral interventions, mindfulness, acceptance and commitment, relaxation training, and coping skills as appropriate to their needs. Emotion regulation training helps the patient distinguish between "sense of danger" and "real danger" and does not automatically consider any physical sign as a sign of cancer return. These skills become especially important when performing periodic tests, imaging, medical visits, or experiencing the experience of other people's illnesses. However, the individual, cultural, and medical differences of survivors, the heterogeneity of measurement methods, and the limitations of some longitudinal studies are among the challenges in this area. Also, the goal of the intervention should not be to eliminate fear completely, as some concern about health after experiencing cancer can be normal, but rather to reduce the severity and dysfunction caused by this fear and increase the individual's ability to live with uncertainty. It is suggested that fear assessment of recurrence and emotion regulation be included in psychological care programs for cancer survivors, and that person-centered interventions be designed based on the type of cancer, treatment conditions, psychological needs, and support resources of each individual. Longitudinal research and clinical trials could also provide more rigorous evidence about the role of emotion regulation in reducing fear of relapse. Overall, strengthening emotion regulation within a psycho-oncology framework can help cancer survivors better manage their difficult emotions, break from the cycle of worry and rumination, become more psychologically adaptable, and improve their quality of life after treatment.