CONTEXT: A popular form of pregnancy physical activity (PA) is prenatal yoga. However, little is known about the intensity and energy cost of this practice. AIMS: To examine the energy cost and intensity level of prenatal yoga. METHODS: Pregnant women in a prenatal yoga class (n = 19) wore a Sense Wear Armband during eleven 60 min classes each, and self-reported demographic variables, height and weight, prepregnancy weight, and PA behaviors and beliefs. Sense Wear Armband data included kilocalories, metabolic equivalent (MET) values, and time spent in various intensities. Descriptive statistics and frequencies were utilized to describe energy expenditure and intensity. RESULTS: Energy expenditure averaged 109 +/- 8 kcals, and the average MET value was 1.5 +/- 0.02. On average, 93% and 7% of classes were sedentary and moderate intensity PA, respectively. CONCLUSIONS: Time spent in a prenatal yoga class was considered to be primarily a sedentary activity. Future research should utilize larger samples, practice type, and skill level to increase generalizability.