Investigate the associations between psychosocial factors and physical activity. Secondary data analysis utilizing baseline data of a large-scale community-based randomized controlled lifestyle behavior intervention. The Special Supplemental Program for Women, Infants, and Children in Michigan, USA. Low-income overweight or obese mothers with young children (N = 740, 65% response rate). Survey data were collected via phone interview. Predictors included self-efficacy, autonomous motivation, emotional coping, and social support. Self-reported leisure physical activity was the outcome variable. Covariates were age, race, smoking, employment, education, body mass index, and postpartum status. A multiple linear regression model was applied. Self-efficacy (β = .32, 95% CI = .11, .52, P = .003) and autonomous motivation (β = .10, 95% CI = .03, .17, P = .005) were positively associated with physical activity. However, emotional coping and social support were not associated with physical activity. Future research should examine the longitudinal association of key psychosocial factors with physical activity.