Background Gestational diabetes is a growing problem worldwide, with risks for both the woman and the baby. Stress has been shown to be linked with diabetes, and therefore research is examining the effect of relaxation on blood pressure. Aim To assess the effect of relaxation on blood glucose and blood pressure in women with gestational diabetes mellitus. Methods This quasi-experimental study was performed with a sample of 80 participants. Fasting blood glucose and systolic and diastolic blood pressure were measured before and after the intervention, which was a 10-week programme of home mind-body and relaxation. Findings Both systolic blood pressure and fasting blood glucose in the control group were significantly higher (P<0.001). Diastolic blood pressure in both groups was not found to be significantly different (P=0.151). Conclusions Relaxation exercises reduce fasting blood glucose and systolic blood pressure in women with gestational diabetes mellitus.