College athletes are at risk for heavy alcohol use, which jeopardizes their general health, academic standing, and athletic performance. Effective prevention programming reduces these risks by targeting theory-based intermediate factors that predict alcohol use while tailoring content to student-athletes. The purpose of this study was to examine the impact of the myPlaybook online prevention program on student-athletes’ social norms, negative alcohol expectancies, and intentions to use alcohol-related harm prevention strategies. NCAA Division II student-athletes were recruited from 60 institutions across the United States to complete myPlaybook and pretest/posttest surveys measuring demographics and targeted outcome variables. Participants were randomly assigned to the treatment group (pretest-program-posttest; final n = 647) or the delayed treatment “control” group (pretest-posttest-program; final n = 709). Results revealed significant program effects on social norms (p < .01) and intentions to use harm prevention strategies (p < .01), while the effect on negative alcohol expectancies was nonsignificant (p = .14). Implications for future research and practice are discussed.