Background: Traumatic birth experiences may lead to serious psychological impairment. Recent studies show that a considerable number of women can develop post-traumatic stress disorder (PTSD). Objectives: The aim of this study was to investigate the effect of cognitive-behavioral therapy (CBT) on PTSD in pregnant women with a history of traumatic childbirth. Methods: This quasi-experimental study was conducted on 80 pregnant women with a history of traumatic childbirth, referring to health centers in Zahedan in 2020. The mothers were selected by a convenience sampling method and divided into two groups (40 mothers in each group) according to the random allocation method. The data were collected using the PTSD questionnaire administered before the intervention and five weeks after the final training session. The intervention group received four sessions of CBT during four weeks, and the control group received only routine pregnancy care. Data analysis was performed by SPSS 22 software using the independent t-test, chi-square test, and paired sample t-test at a significant level of < 0.05. Results: The results of the study showed that the mean post-traumatic stress score of pregnant women before CBT in the intervention and control groups was 27.90 ± 10.91 and 24.97 ± 14.85, respectively, and it changed to 15.25 ± 4.08 and 26.25 ± 11.56, respectively, after the intervention. Independent t-test showed that the mean scores of post-traumatic stress of pregnant women in the two groups were not significant before education (P = 0.31), but it was significant after it (P = 0.0001). Conclusions: CBT can have significant effects on reducing the severity of PTSD in pregnant women with a history of traumatic childbirth. Thus, it is recommended to include this type of educational intervention in the care program of pregnant women with a history of traumatic childbirth.