Objectives: The aim of this study was to assess whether Horticulture Therapy (HT) is effective for the improvement of the conceptual organization function, memory and psychological symptoms of chronic depressed male outpatients. Methods: 30 outpatients were chosen by the convenience sampling method. They were assigned to two groups, namely the experimental and the control group, by the random assignment method (each group comprising of 15 people). Outpatients were evaluated for before and after intervention by Rey–Osterrieth complex figure, and on the Depression Anxiety and Stress Scale, DASS-44. Results: After ten sessions of horticultural therapy, the patients scores on conceptual organization function, memory, depression, anxiety, and stress improved significantly. Discussion: Although horticultural therapy improved outpatients scores on conceptual organization function, memory, depression, anxiety, and stress, future study is needed, especially by engaging more patients.