The authors examined the efficacy of Web-assisted instruction for promoting the use of social cognitive theory (SCT) strategies related to physical activity. They recruited college students attending health courses. The authors created 3 groups (Web-assisted, comparison, and control) based on the course structure. The Web-assisted group received information on exercise and fitness and a Web-based program (treatment, n = 127); 7 sections received the same exercise and fitness information as the treatment condition, but no Web-based program (comparison, n = 118); and 6 sections received information in unrelated areas (control, n = 178). The Web-based program consisted of 9 Web assignments (1 per week) that targeted key SCT variables. Satisfaction with the Web-based program was high. Use of self-regulation strategies was significantly higher at posttest in the treatment group than it was in the other groups. Knowledge concerning the skills taught by the Web assignments was significantly greater in the treatment group than it was in the comparison group. The results of this study demonstrate that a Web-based instructional program has a positive impact on knowledge and skills related to SCT strategies for changing physical activity behavior. (Contains 4 tables.)