Objective: This study was conducted to determine the effect of cognitive-behavioral stress management (CBT) on reducing psychological stress in diabetic pregnant women.Method: This randomized controlled trial applied through pretest and post-test with control group was conducted on 88 eligible women with gestational diabetes. Women who had a stress score more than 15, randomly assigned to intervention or control groups. Intervention group received stress management training within six two-hour sessions for three weeks. Stress and FBS were measured before intervention and two weeks after the last session. Data were analyzed using the SPSS version 19.0. Results were analyzed using chi-square, paired t test and independent sample t test.Results: In CBT training group, stress significantly decreased two weeks after the training (p<0.001). In the control group, the stress scores were significantly different before and after the intervention and women had a significant increase in the stress scores (p=0.028). There was a significant difference between two groups in stress scores, two weeks after intervention (p=0.001).Conclusion: Cognitive-behavioral stress management reduces stress in women with gestational diabetes and reducing stress may also improve the pregnancy outcomes, especially whose glycemic along with stress is not adequately controlled by medication.