Background: The purpose of this study was to examine the feasibility and effectiveness of a web-based intervention to promote physical activity and self-worth among working mothers. Methods: Participants (N = 69) were randomly assigned to receive a standard web-based intervention or an enhanced intervention that included group dynamics strategies to promote engagement. The 8-week intervention was guided by self-determination theory. Each week, participants were instructed to complete 3 tasks: listen to a podcast related to well-being, complete a workbook assignment, and communicate with other participants on a discussion board. Participants in the enhanced condition received an additional weekly task to enhance group cohesion. Data were collected at baseline, week 8, and week 16. Results: Physical activity (P < .001, eta(2) = 0.35) and self-worth (P < .001, eta(2) = 0.39) increased significantly in both groups following the intervention, and introjected (P < .001, eta(2) = 0.30) and external motivation (P = .04, eta(2) = 0.10) decreased. Website use declined across the 8-week intervention in both groups (P < .001, eta(2) = 0.48); however, discussion board use was higher in the enhanced condition (P = .04, eta(2) = 0.21). Conclusions: These findings suggest web-based interventions can improve physical activity and self-worth among working mothers. Group dynamics strategies only minimally enhanced user engagement, and future studies are needed to optimize web-based intervention designs.