Background and Objectives: Cancer survival rate increased during the last 3 decades, following medical advances and improvement of therapeutic protocols to treat children with cancer. Contribution to childhood activities is essential to the growth and development of children, regardless of their ability and disability. However, there is no information about the problems and requirements of childhood activities in children with cancer undergoing cancer therapy. The purpose of this study is to provide information about the occupational performance needed in children with cancer. Methods: A cross-sectional study was conducted to evaluate high priority problems in occupational performance in children with cancer. Occupational performance needs and priorities were determined by a semi-constructed interview using the Canadian occupational performance measure (COPM). The obtained data were encoded and statistically analyzed. Results: Based on the problems noted by the children with cancer, a total of 141 problems were selected in the occupational performance areas out of which 37 codes were extracted. Results of the current study indicated that based on COPM, among 3 main occupational performance areas, the most problematic area belonged to self-care (49.64%), then productivity and leisure time (26.95% and 23.40%, respectively). Conclusion: Results of previous as well as the current studies indicated that children with cancer, due to the complications of the disease and side-effects of the therapies, face some functional problems in their daily life activities, which emphasizes the need for occupational therapy practices in order to improve the patients' QoL.