This study investigated the effectiveness of cognitive – behavioral therapy, drug tehrapy, and their combination in treating obsessive – compulsive disorder. Twenty one patients with obsessive – compulsive disorder were randomly assigned to three groups: cognitive – behavioral , clomipramine, and combined cognitive – behavioral and clomipramine treatment groups. Treatment outcomes were analyzed with a 3x3 split-plot design using univariate analysis of variance with repeated measures. Results revealted significant differences in all pre-treatments dependent variables, that is obsessive – compulsive symptoms, anxiety, depressed mood, belifs and sysfunctional attitudes in both cognitive – behavioral and combination therapy groups. But clomipramine treatment group only showed significant improvement in depressed mood. Combination of clomipramine and cognitive behavioral techiniques was more effective than clomipramine alone but no significant differences wer found between combination therapy and cognitive – behavioral groups.