This study examined the effects of a content-based instruction (CBI) course on Korean EFL students` self-perceived language skill, thinking skill, and affect. A questionnaire was designed to measure students` attitudes toward CBI and its benefits and problems. Twenty four college students participated in the survey, based on which follow-up interviews were conducted. The findings indicated that the students perceived the CBI course as beneficial for developing listening, speaking and note-taking skills. They also believed that CBI facilitated the acquisition of content knowledge and critical thinking skills. It is interesting to note that the students considered discussion as more useful and effective than lectures. They reported that their learning interest increased as a result of taking the CBI course. While the students perceived that CBI is effective in acquiring language skills and content knowledge, they cautioned that differences in language proficiency could negatively influence the effectiveness of CBI.