OBJECTIVES: While several studies on the preventive and therapeutic effects of prenatal yoga (maternity yoga) have been reported in recent years, there has been no systematic review on the effects of prenatal yoga based on randomized controlled trials (RCT). The purpose of this study, therefore, was to systematically review the literature to clarify the effects of prenatal yoga in RCT focusing on the contents of the intervention, the intervention means, and the frequency of practice. METHODS: The literature search was performed using the electronic database, PubMed. The inclusion criteria were RCT, pregnant women, and yoga intervention. RESULTS: In total, 54 citations were found; of these, eight studies (10 reports) were included in the final analysis. In four studies on healthy pregnant women, significant improvement in pain and pleasure at delivery, duration of delivery, perceived stress levels during pregnancy, anxiety levels, depression, pregnancy-related experiences, quality of life, and interpersonal relationships were compared to those in the control group. In two studies on depressed pregnant women, one reported that depression, anxiety levels, anger levels, leg pain, and back pain significantly improved with yoga, while the other found no differences from the control group. In one study of high-risk pregnant women with morbidity factors such as obesity or advanced age, yoga resulted in significantly fewer cases of pregnancy-induced hypertension, gestational diabetes, and intrauterine growth restriction, as well as a decrease in perceived stress levels. In one study on pregnant women with pelvic pain, the median pain score was lower in the yoga group. Regarding the contents of the intervention, while the two studies for depressed pregnant women only included physical postures, the remaining six studies also included breathing technique and meditation. Interventions were performed using lectures by instructors alone or together with self-teaching. The frequency of the intervention varied within each study. CONCLUSION: The findings suggest that prenatal yoga may help reduce pelvic pain. It may also improve mental condition (stress, depression, anxiety, etc.), physical condition (pain and pleasure at the delivery, etc.), and perinatal outcomes (obstetrical complications, delivery time, etc.). However, further studies are needed. The contents of the intervention, the intervention means, and the frequency varied with each study. Thus, it is necessary to further examine the content of effective interventions, intervention means, and frequency that suit participant's characteristics and each outcome. Further research in this field, particularly randomized controlled trials, is merited.