Background and Purpose:The incidence of cancer in children is a stressful event that, in addition to causing various health problems for the family, may also have different physical and psychological consequences for the child. Depression is one of the most important comorbid psychological symptoms with cancer, which has been widely reported in both studies and clinical observations in people with the disease. The purpose of this study was to investigate the effect of emotion regulation training on depression in children with cancer Methods: The method of this study was quasi-experimental with pre-test and post-test. The statistical population of this study included all children aged 8 to 12 years (boys and girls) with cancer who were admitted to the medical centers of Shahid Bahrami Children's Hospital in 2016. Ten children from these health centers were selected by convenience sampling and received emotion regulation intervention program in nine 30-minute sessions. Research data were collected by parents and teacher forms of the Child Behavioral Inventory Questionnaire (Achenbach and Rescorla, 2001) during the pre-test and post-test stages. Data were analyzed using dependent t-test. Results: Dependent t-test results showed that the depression score of children in post-test was significantly decreased compared to pre-test; therefore, emotion regulation training had a significant effect on reducing depression in children with cancer (P <0.001). Conclusion:Based on the findings of the present study, it can be concluded that the intervention program used in this study has been able to reduce the depression syndrome in children with cancer by enhancing positive emotion regulation skills and reducing negative skills. In addition, increasing the use of positive emotion regulation strategies in children with cancer will help them to accept existing conditions of the disease and increase their cooperation, thereby facilitating their treatment in the hospital.