Siblings of children with cancer often experience negative feelings, and art intervention can help them express their feelings and overcome hardships. This study aimed to develop an Art Intervention Program to improve the psychological adaptation of siblings of children with cancer and to evaluate its effects. Participants were seventeen 7- to 10-year-old siblings of children with cancer. The program comprised 12 sessions conducted once a week. The effects of the intervention were assessed in terms of self-esteem, anxiety, depression, and problem behavior. Self-esteem significantly improved after intervention compared with pretest. Children showed improved scores in externalizing problems and total behavior problems; however, anxiety and depression did not change. The study results indicated that the art intervention program helped improve the self-esteem and helped reduce somatic symptoms, aggressiveness, externalizing problems, and emotional instability among problem behaviors of siblings of children with cancer. However, the study was limited by its small sample size and the lack of a control group. Therefore, the study design allows no firm conclusions, and a randomized controlled trial is needed to investigate the effectiveness of the program.