Objectives: The high rate of comorbidity between bipolar and obsessive-compulsive disorders can be due to common transdiagnostic processes. Therefore, the aim of the present study was to determine the role of cognitive emotion regulation strategies (CERS), anxiety and impulsivity, in developing and maintaining bipolar and obsessive-compulsive disorders. Method: Twenty five patients with bipolar disorder (11 females and 14 males), 25 with comorbid bipolar disorder and obsessive-compulsive disorder (12 females and 13 males) and 25 healthy participants (13 females and 12 males) were selected using convenience sampling method. To collect the data, participants were administered Cognitive Emotion Regulation Questionnaire (CERQ-short), Impulsivity Questionnaire, and Beck Anxiety Inventory (BAI). Data were analyzed using multivariate analysis of variance. Results: Results showed that compared to healthy participants, patients with comorbid bipolar and obsessive-compulsive disorders use more self-blaming and other-blaming maladaptive cognitive emotion regulation strategies (p<0.01). Compared with normal subjects, both patient groups utilized more rumination and catastrophizing strategies, the scores of the patients with comorbid disorder were higher than bipolar patients without comorbid on these strategies disorder (p<0.01). Both patient groups used more adaptive positive refocusing strategies, reappraisal, and less putting into perspective compared to healthy controls(p<0.01). Also, both patient groups scored higher than healthy controls in anxiety, attentional/cognitive impulsivity, motor impulsivity and non-planning impulsiveness; while patients with comorbid disorder scored higher than patients with only bipolar disorder (p<0.01). Conclusion: Anxiety, impulsivity and some of the cognitive emotion regulation strategies (self-blaming, rumination, catastrophizing) are transdiagnostic processes and play critical roles in developing and maintaining bipolar disorder with and without obsessive-compulsive disorder.