Studies have demonstrated that postnatal women are at high risk for physical inactivity and generally show lower levels of leisure-time physical activity (LTPA) compared to prepregnancy. The overall purpose of the current study was to investigate social cognitive correlates of LTPA among postnatal women during a 6-month period following childbirth. A total of 230 women (mean age = 30.9) provided descriptive data regarding barriers to LTPA and completed measures of LTPA and self-efficacy (exercise and barrier) for at least one of the study data collection periods. A total of 1,520 barriers were content analyzed. Both exercise and barrier self-efficacy were positively associated with subsequent LTPA. Exercise self-efficacy at postnatal week 12 predicted LTPA from postnatal weeks 12 to 18 (β = .40, R (2) = .18) and exercise self-efficacy at postnatal week 24 predicted LTPA during weeks 24-30 (β = .49, R (2) = .30). Barrier self-efficacy at week 18 predicted LTPA from weeks 18 to 24 (β = .33, R (2) = .13). The results of the study identify a number of barriers to LTPA at multiple time points closely following childbirth which may hinder initiation, resumption or maintenance of LTPA. The results also suggest that higher levels of exercise and barrier self-efficacy are prospectively associated with higher levels of LTPA in the early postnatal period. Future interventions should be designed to investigate causal effects of developing participants' exercise and barrier self-efficacy for promoting and maintaining LTPA during the postnatal period.