Background: Vicarious learning is one of the fundamental sources of self-efficacy that is frequently employed in educational settings. However, little research has investigated the effects of competition on students' writing self-efficacy when they engage in vicarious learning. Aim: This study compared the effects of competitive and non-competitive classrooms on students' writing self-efficacy when they engaged in vicarious learning. Sample: The participants were 71 grade 7 students in Hong Kong. Method: Using prior writing performance for stratified random sampling, students were assigned either to a competitive or a non-competitive classroom. Students learned how to compose similes and metaphors in Chinese. Results: In the competitive classroom, students' self-efficacy decreased when they engaged in vicarious learning. In the non-competitive classroom, students' self-efficacy did not show a significant change when they engaged in vicarious learning. Conclusion: The findings suggested that when students engaged in vicarious learning in a competitive classroom, their self-efficacy might be threatened. Implications for efforts to design constructive context for vicarious learning are discussed.