Background. The family and home environment is an influential antecedent of childhood obesity. The purpose of this study was to pilot test The Enabling Mothers to Prevent Pediatric Obesity through Web-Based Education and Reciprocal Determinism (EMPOWER) intervention; a newly developed, theory-based, online program for prevention of childhood obesity. Method. The two-arm, parallel group, randomized, participant-blinded trial targeted mothers with children between 4 and 6 years of age. Measures were collected at baseline, 4 weeks, and 8 weeks to evaluate programmatic effects on constructs of social cognitive theory (SCT) and obesity-related behaviors. Process evaluation transpired concurrently with each intervention session. Results. Fifty-seven participants were randomly assigned to receive either experimental EMPOWER (n = 29) or active control Healthy Lifestyles (n = 28) intervention. Significant main effects were identified for child physical activity, sugar-free beverage consumption, and screen time, indicating that both groups improved in these behaviors. A significant group-by-time interaction was detected for child fruit and vegetable (FV) consumption as well as the SCT construct of environment in the EMPOWER cohort. An increase of 1.613 cups of FVs (95% confidence interval = [0.698, 2.529]) was found in the experimental group, relative to the active control group. Change score analysis found changes in the home environment accounted for 31.4% of the change in child FV intake for the experimental group. Conclusions. Child physical activity, sugar-free beverage consumption, and screen time improved in both groups over the course of the trial. Only the theory-based intervention was efficacious in increasing child FV consumption. The EMPOWER program was robust for inducing change in the home environment leading to an increase in child FV intake (Cohen's "f" = 0.160).