The present study was conducted to develop a family-based art therapy method adjusted to hospital condition, and evaluate its effectiveness on the children’s coping with cancer. The present research is a single-subject study (A-B) as a kind of experimental research. The statistical population of the study consisted of all children aged 9-14 years old admitted to Children Medical Center (CMC) from November 2018 to February 2019 that among them, five children were selected by purposeful sampling. Each child accompanied with her/his mother received eight family-based art therapy sessions. The tools of the present study were Checklist of Bio-Psycho-Social Expressions of Incompatibility in Hospital-BPSEIH (Purrezaian, Besharat, Koochakzadeh, & Farahani, 2019) and Children’s Coping Strategies Checklist-revision 1 (Ayers & Sandler, 1999). Research data were analyzed using specific charts and tables for single-subject designs. In addition, the effect size (ES) and the reliable change index (RCI) were also reported. The findings showed that family-based art therapy reduced the expressions of incompatibility and avoidance strategy (P < 0/05) on the one hand, and increased support seeking strategy (P<0/05) on the other, significantly. According to the findings, it can be concluded that family-based art therapy can reduce the incompatibility of children with cancer in hospital and change their coping strategies. Therefore, this method can be considered as one of the useful and practical psychotherapies in the hospital especially for children with cancer.