: The purpose of this research is to determine the effectiveness of filial therapy on the primary maladaptive schemas of children with cancer. The present research method is a semi-experimental one-subject A-B-A type. The sample subjects were three children with cancer in the age range of 8-13 years old along with their mothers who visited Dr. Sheikh Hospital in Mashhad and were selected by purposeful sampling. Subjects were individually treated for 8 sessions in the process of filial therapy (Landreth, 2006). Before and after the treatment, schema inventory for children (SIC) was implemented on the sample. The clinical results were compared before and after the intervention, and the obtained information was analyzed based on eye charts, effect size and recovery percentage. The results showed that this treatment is effective in improving the initial maladaptive schemas of children with cancer. The effect size was obtained for loneliness domain (3.57), misbehavior domain (6.81), defect domain (6.06), vulnerability domain (5.34) and stubborn standards domain (3.30). According to the results of this research, it can be said that filial therapy is effective on the primary maladaptive schemas of children with cancer and can be used clinically.