Background: Borderline personality disorder (BPD) might be conceptualized as belonging to the bipolar disorder spectrum. For this purpose, we compared these disorders’ attachment styles, intimate relationship, and anger experience. Objectives: Objectives of the current research were investigating of attachment style, quality of intimate relationship, and anger experience in patients with porderline personality and bipolar-II disorders and comparing these variables in these groups. Methods: The method of research was comparative. The sample consisted of 37 BPD and 41 BP-II outpatients that were selected through convenience sampling method. They were requested to answer “Attachment Style Questionnaire”, “Quality of relationship inventory” and “Multidimensional Anger Inventory”. Results: The t-test showed that there was no significant difference between BPD and bipolar disorder Type II (BP-II) groups in anxious and secure attachment styles. However, BPD patients showed higher levels of avoidant attachment styles compared to the BD-II patients. In addition, there was no significant difference between the 2 groups in the quality of intimate relationship and anger experience in general. However, BPD and BD-II patients had a significant difference in “conflict with friends”, “conflict with partner”, and “anger arousal” subscales, in a way that BPD patients had higher scores on these subscales. Conclusions: The results of our study suggest that insecure attachment style is the common underlying psychopathology of both BPD and Bipolar disorders that leads to similar intimate relationships and anger experience. These findings support the re -conceptualization of BPD in the Bipolar spectrum.