Background: Post-traumatic stress disorder (PTSD) can lead to complications such as depression and grief, which are more prevalent in veterans than in the general population. Recently, art-making, including mandala coloring, has gained attention as a potential treatment for PTSD patients.

Methods: This randomized clinical trial was conducted on 84 male veterans diagnosed with PTSD and hospitalized at the Milad Psychiatric Center in Tehran, Iran. The patients were recruited using a convenience sampling method and were assigned to either the mandala coloring group or the free coloring group. The Post-Traumatic Stress Disorder Checklist DSM-5 and the Oxford Happiness Scale were used to collect data. The intervention group colored mandala designs, while the control group colored squares freely. Coloring was done twice a week for three weeks.

Results: The mean baseline happiness scores did not differ significantly between mandala coloring group and free coloring group (p = 0.376). However, at the end of study, happiness scores were significantly higher in mandala coloring group than in free coloring group (p < 0.001). After the intervention, happiness score of both groups increased significantly (p < 0.001).

Conclusion: Both coloring methods increased veterans' happiness scores; however, mandala coloring was more effective than free coloring. It is recommended that art-making be added to conventional treatments for veterans with PTSD.

Trial registration: This study was registered in Iranian Registry of clinical trials (No. IRCT20210604051491N1, 29/08/2021).