Obsessive-Compulsive Disorder (OCD) is one of the most common and debilitating psychological disorders. This quasi-experimental study aimed to investigate the effect of three psychological interventions, including cognitive-behavioral therapy (CBT), existential therapy (ET), and transactional analysis (TA), which have been performed simultaneously on Obsessive-Compulsive Disorder (OCD) patients in Milad Hospital. In this study, 60 patients were randomly assigned to experimental and control groups. The measures used included the Yale-Brown Obsessive-Compulsive Scale. The intervention program of cognitive-behavioral therapy, existentialism, and interaction behavior analysis consisted of eight 60-minute sessions performed only on the experimental group. The results of covariance analysis showed that the combined program of CBT, ET, and TA is effective in the obsessive-compulsive beliefs of patients with OCD (P <0.01). According to the results of the present study on the effectiveness of the intervention program, training can be combined with CBT, ET, and TA as suitable option in designing psychological treatment plans for patients with OCD.