ABSTRACT In this mixed-methods study, we investigated the relationship between instructional approach, students’ self-efficacy beliefs, and students’ English language proficiency, as well as the perceptions of the instructor and students regarding problem-based learning (PBL) in a College English course in China. Using path analysis, we assessed the effectiveness of PBL as compared to traditional lecture-based instruction, focusing on PBL’s impact on Chinese college students’ self-efficacy beliefs and English proficiency. We also explored the perceptions of both instructors and students regarding PBL using their qualitative feedback. Two classes of College English (N = 57) at a tier-one university in China were randomly assigned to either a PBL or a traditional lecture condition for one semester, while controlling for students’ initial English placement test scores. The results indicated that PBL instruction fostered students’ English proficiency, and students’ self-efficacy positively impacted their English proficiency, as measured by a national English standardized test. However, PBL did not impact students’ self-efficacy beliefs. Both the instructor and students held positive attitudes towards PBL instruction in the English classroom, and students made recommendations for activities and ways to improve. Further investigation of PBL’s effectiveness is needed to support English as a foreign language students’ language acquisition in a global context.