Background: Bipolar disorder is considered one of the most debilitating mental illnesses. While most studies focus on symptoms, recurrences, and mood states, functioning is becoming an increasingly important research focus. This study aimed to assess the effect of Interpersonal and Social Rhythm Therapy on functional outcomes among clients with bipolar disorders. Methods: A prospective quasi-experimental study was conducted on a purposive sample of 27 outpatients diagnosed with bipolar disorders at the Main University Hospital's psychiatric outpatient clinics. Tools: Interpersonal Problem Areas Rating Scale, Social Rhythm Metric Scale SRM-II-5, and The Multnomah Community Ability Scale were used. Results: There was a statistically significant improvement in the total score of the Multnomah Community Ability Scale from the first measurement compared to after the intervention and one month later (55.52 SD=7.42, 68.67 SD=7.13, 68.74 SD=7.24, respectively), with a large effect size of 90.2%. Significant improvements were also observed in the mean scores of the Social Rhythm Metric Scale SRM-II-5 from (2.91 SD= 1.32) to 4.89 SD= 1.23, and 5.04 SD=1.21 respectively immediately after the intervention and one-month later, with a large effect size of 83.2%.Conclusions: Interpersonal and Social Rhythm Therapy was found to be effective in improving functional outcomes and regularizing social rhythm among patients with bipolar disorder. These improvements can enhance patients' social roles, helping them control mood disturbances associated with social rhythm disruption and loss of social roles. Therefore, psychiatric nurses might consider incorporating IPSRT intervention as a crucial component in the care of patients with bipolar disorders.