Aim: To examine how the occupational performance (OP) and participation levels of children with cancer changed during the COVID-19 pandemic. Methods: Sixty-seven children with cancer (aged 6-12 years) completed the Canadian Occupational Performance Measure by giving information about their OP and participation, and their parents completed the Child and Adolescent Scale of Participation via online interview techniques. Evaluations were repeated twice in April and September 2020 to determine the change in OP and participation levels of children with cancer due to the COVID-19. Results: OP of children with cancer decreased significantly (Z=-7.02, p < 0.001) during the pandemic period. The home participation of these children did not change significantly (Z=-0.98, p = 0.32) before and during the pandemic; and was limited in both periods. Community participation decreased significantly (Z=-4.84, p < 0.001) from limited level to very limited level. Conclusions: Findings emphasize the need to increase the levels of OP and participation levels of children with various types of cancer due to the ramifications of the COVID-19 pandemic.