This study evaluated the efficacy of two Web-based interventions aimed at reducing heavy drinking in mandated college students. Mandated students were randomly assigned to one of two conditions: Web-based personalized normative feedback (WPNF) or Web-based education (WE). As predicted, results indicated that mandated students in the WPNF condition reported significantly greater reductions in weekly drinking quantity, peak alcohol consumption, and frequency of drinking to intoxication than students in the WE condition at a 30-day follow-up. Although not statistically significant, there was a similar trend for changes in alcohol-related problems. Mandated students in the WPNF group also reported significantly greater reductions in estimates of peer drinking from baseline to the follow-up assessment than students in the WE group. In addition, changes in estimates of peer drinking mediated the effect of the intervention on changes in drinking. Findings provide support for providing Web-based personalized normative feedback as an intervention program for mandated college students.