This retrospective quasi-experimental study evaluated the effectiveness of an anger management group program for clients with mental health problems. The program, based on the cognitive-behavioral approach, was offered by outpatient mental health occupational therapy services of a community general hospital. Sixty-four clients, about 59% diagnosed with depressive disorder, enrolled in the program and participated in the study. The pre-treatment and post-treatment scores of the participants on the Anger Control Inventory and the State-Trait Anger Expression Inventory were compared. The results indicated significant reduction in the overall experience of intense anger, improvement in cognitive and behavioural coping mechanisms, and significant improvement in anger control after treatment. Most respondents (90%) found the program definitely helpful. The pace of the program and the variety of learning activities were identified as areas for improvement. The results showed the program had positive impact on anger management. Useful suggestions were identified for continuous quality improvements of the program.