Abstract Objective Gestational diabetes can cause maternal and neonatal morbidity. Psychological factors, especially stress, play a meaningful role in diabetes management. Therefore, the present study aimed to investigate the effect of Mindfulness-Based Stress Reduction counseling on blood sugar and perceived stress in women with gestational diabetes. Methods The present quasi-experimental interventional study was performed on 78 women with gestational diabetes. In the intervention group, a Mindfulness-Based Stress Reduction counseling program was conducted by the researcher in 8 sessions of 90 minutes twice a week. The Cohen stress questionnaire was filled in both groups. Also, fasting blood sugar and 2-hour blood sugar levels were measured in both groups. Statistical analysis was performed using the independent T-Test, the paired T-Test, the Mann-Whitney and Wilcoxon Tests using IBM SPSS Statistics for Windows version 20 version (IBM Corp., Armonk, NY, USA). Results The mean age of pregnant women in the intervention group was 28.84 ± 6.20 years old and 29.03 ± 5.42 years old in the control group. There was a significant mean difference between the fasting blood sugar score (p= 0.02; - 6.01; and - 11.46) and the 2-hour fasting blood sugar score (p< 0.001;12.35; and - 5.3) and the perceived stress score (p< 0.001; 35.57; and - 49.19) existed between the intervention and control groups after the intervention. Conclusion The results of the present study showed that mindfulness-based stress reduction counseling is effective in reducing blood sugar levels and reducing perceived stress in women with gestational diabetes treated with diet.