Objectives: In this study, we aimed to assess the incidence rate of adverse drug reactions (ADR) to chemotherapeutic agents and related problems in hospitalized pediatric patients diagnosed with cancer who referred to Mahak hospital in Tehran. Methods: All information about 125 children younger than 18-years-old who experienced ADR during their chemotherapy period (from March 2008 to March 2020) in Mahak Pediatric Cancer Treatment and Research Center (MPCTR) was collected and analyzed in SPSS-25. Results: Most of patients (approximately 65%, n=81) were male and the mean age of both genders was approximately 6.6 years of old. In addition, leukemia was the most common cancer type followed by Central Nervous System tumor. In terms of adverse events, skin and subcutaneous disorders occurred in 74 cases of 125, whereas nervous system, Immune system disorders and musculoskeletal related disorders were the least common events each occurring only in four cases. According to Naranjo’s Probability Scale, most ADRs were evaluated as probable in relation with administrated drug (61.60%) and 56.80% of reactions were determined as mild. Furthermore, the commonest ADRcausative drugs were L-asparaginase followed by carboplatin (together more than 56% of all cases. Conclusion: The overall incidence of ADR amongst children diagnosed with cancer in our retrospective study was 3.68 %. Additionally, leukemia treatment regimen including L-asparaginase seems to be significantly vulnerable to induce ADRs in pediatric ward. Finally, there is a crucial need for monitoring pediatric patients during treatment process in order to reduce the risk of ADR occurrence.