Effects of a mirrored exercise environment and body image concerns on changes in exercise-induced feeling states and self-efficacy were examined among 58 sedentary women (mean age = 20.7 years). Participants performed a 20-min bout of exercise in front of either a mirrored or a nonmirrored wall. Feeling states and self-efficacy were measured pre- and postexercise. Multilevel linear modeling indicated that regardless of their level of body image concern, women in the mirrored condition felt worse after exercising than women in the unmirrored condition. There were no effects of the environment or body image on self-efficacy. Results are consistent with predictions of objective self-awareness theory and have implications for promoting exercise among sedentary women.