Introduction: There is much evidence regarding the comorbidity of obsessive-compulsive disorder (OCD) and bipolar disorder (BD). Therefore, this study was done to elucidate the correlation between severity of mixed and manic phases of BD and severity of obsessive-compulsive symptoms in comorbidity of these two disorders.
 Materials and Methods: In this descriptive study, 30 patients admitted in mixed or manic episodes of bipolar disorder type I in Taleghani and Imam Hossein Hospitals in Tehran in 2011, were evaluated with SCID-I for OCD and if OCD were confirmed, the patients were included in this study. Then Young Mania Rating Scale, Hamilton Rating Scale for Depression, Yale-Brown Obsessive Compulsive Scale and demographic questionnaires were completed for all these patients. The severity of mixed and manic phases and also severity of obsessive-compulsive symptoms in the first week of admission, at the time of discharge and one month after discharge were evaluated. Data were analyzed using descriptive statistics, repeated measure, t- test, Wilcoxon, and Pearson correlation by SPSS.19 software.
 Results: Significant statistical correlation between severity of obsessive-compulsive symptoms and Hamilton Rating Scale for Depression during admission and at the time of discharge was observed only in mixed phase (respectively
 P=0.005 and P=0.029).
 Conclusion: Significant correlation between severity of obsessive-compulsive symptoms and depressive component of mixed phase of bipolar disorder can show the stronger correlation between severity of obsessive compulsive disorder and depressive symptoms or depressive episodes of bipolar disorder. This could help us setting appropriate treatment strategies.