The aim of this study was to investigate the effects of peer instruction on college students' conceptual learning, motivation, and self-efficacy in an algebra-based introductory physics course for nonmajors. Variables were studied via a quasi-experiment, Solomon four-group design on 123 students. Treatment groups were taught by peer instruction. Control groups were taught by traditional didactic lecture method. To assess the effects of peer instruction, students were administered Force Concept Inventory and Motivated Strategies for Learning Questionnaire. Factorial analyses indicated that the treatment groups acquired significantly more conceptual learning, and were significantly more self-efficacious than students in the control groups. It was found that there were no significant differences in motivation between groups. (Contains 1 figure and 7 tables.)