Background: Pregnancy may be accompanied by serious physiological and psychological changes as it is a stressful period in a woman's life. So, this study was conducted to determine the effect of progressive muscle relaxation on pregnant women's general health. Materials and Methods: In this clinical trial, 60 primigravida women admitted to the prenatal clinic of selected hospitals in Iran constituted the study population. Using purposive sampling method, the level of general health of the women was measured with General Health Questionnaire-28 (GHQ-28). Then, the samples were randomly divided into control and experimental groups. Three 1.5–2 h relaxation training sessions were held for the experimental group. After 8 weeks, the level of general health of both groups was measured again. Finally, the collected data were analyzed using Chi-square and paired t-test (P < 0.05). Results: Total mean score of general health of the experimental group and the control group before the intervention was 35.83 (6.92) and 29.46 (8.3), respectively, and after the intervention, the respective scores were 20.2 (5.61) and 27.85 (8.24). Although after the intervention both groups showed an increased level of general health, the difference in general health between before and after intervention was significant in the experimental group (P < 0.001). Furthermore, comparison of variations in mean scores of general health level before and after intervention in the two groups showed a significant difference (P < 0.001). Conclusions: Given that the results showed the effectiveness of progressive muscle relaxation on pregnant women's general health, the prenatal clinics can include a training program for progressive muscle relaxation in the routine training programs for pregnant women.