Background: Prevalence of body image disorder in postpartum period, especially in primiparous women is relatively high. This study aimed to determine the effectiveness of cognitive behavioral group therapy based on the cash's eight-step model in body image of primiparous women. Objective: This study aimed to determine the effectiveness of cognitive behavioral group therapy based on the cash's eight-step model in body image of primiparous women. Methods: This research was a pretest-posttest quasi-experimental study in which, 61 primiparous women referring to health centers in Zahedan were selected according to convenience sampling method and randomly assigned into intervention and control groups. The multidimensional body-self relations questionnaire (MBSRQ) was used to collect data. The intervention group received group cognitive behavioral body image therapy based on the Cash model and the control group remained pending. After six weeks, both groups completed the MBSRQ again. Data analysis was performed using descriptive statistics and analysis of covariance in SPSS 22. Results: Analysis of covariance showed that the mean scores on appearance evaluation (P = 0.0001), body areas satisfaction (P = 0.0001), and the total score of body image (P = 0.0001) in the intervention group were significantly higher than those in the control group. However, in terms of appearance orientation, fitness evaluation, fitness orientation, and subjective weight, there was no significant difference between the two groups (P > 0.05). Conclusions: Due to the effectiveness of cognitive behavioral therapy based on Cash model in primiparous women's body image, it is recommended to use this method of consultation in health care programs after child birth to improve the women's body image and prevent subsequent psychological problems.