Background & aim: Rumination and poor interactive quality are among the most common psychological problems of women suffering from postpartum depression. Therefore, the purpose of this research was to determine the effectiveness of a one-day workshop based on cognitive behavioral therapy on rumination and interactive quality of women suffering from postpartum depression. Methods: It was a semi-experimental research design of pre-test-post-test type with a control group and a follow-up stage. The statistical population of this research included all women suffering from postpartum depression in Salmas city who were referred to health centers in 2022 to receive psychological services. The sample size includes 50 subjects (25 in the experimental group and 25 in the control group) from the statistical population selected by available sampling method and they were randomly divided into two groups, the control group and the experimental group. For the experimental group, a one-day workshop based on cognitive behavioral therapy was implemented, while the control group did not receive training. Two weeks after the end of the training sessions, the scale of rumination responses and the relationship quality scale were completed as a post-test and follow-up after two months. The data were analyzed using the analysis of variance test with repeated measurements and SPSS-26 software. Results: The average rumination scores in the pre, post and follow-up stages were 42. 16, 36. 60 and 36. 96, respectively in the experimental group and 40. 12, 41. 36 and 41. 44 in the control group, respectively. Also, the average interactive quality scores in the pre, post and follow-up stages in the experimental group were 20. 40, 28. 28 and 29. 40, respectively and in the control group were 21. 28, 20. 72 and 20. 32, respectively. The results of analysis of variance with repeated measures showed that the one-day workshop based on cognitive behavioral therapy had a significant effect on rumination and interactive quality in the post-test and follow-up stages (p<0. 001). Conclusion: Findings of this study provide useful information about one-day workshop based on cognitive behavioral therapy and counselors and psychologists can use this intervention to improve rumination and interactive quality of women with postpartum depressive disorder.