Introduction: Because of the high similarity of symptoms and clinical characteristics between borderline personality and bipolar spectrum disorders particularly bipolar-II disorder, some investigators reclassified borderline personality disorder on bipolar spectrum and considered common etiology for two disorders. In the present study in order to evaluate this hypothesis, intimate relationship and anger experience in borderline personality and bipolar-II disorders were compared. Materials and Methods: A sample consists of 27 borderline personality and 31 bipolar-II disorder outpatients, who were referred to the Psychiatric Ward of Kamkar-arabnia hospital in Qom, Iran were selected through convenience sampling method. They answered to "Quality of relationship inventory" (QRI) and "Multidimensional Anger Inventory" (MAI). The mean of variables in both groups were compared by Independent T-test. Results: The results of Independent T-test showed that there was no significant difference between two groups in quality of intimate relationship and anger experience. However, borderline and bipolar-II patients had a significant difference in conflict subscale of QRI and anger arousal subscale of MAI. Compared to the bipolar-II patients, borderline patients were obtained higher scores on both subscales. Conclusion: No significant difference between quality of intimate relationship and anger experience in borderline and bipolar-II groups may suggest authenticity of the hypothesis that borderline disorder belongs to bipolar spectrum and both disorders might have common etiology.