The present study analyzes learners' self-efficacy beliefs and self-regulated learning strategy use in an L2 English learning context, mainly focusing on Korean high school students. One-hundred and seventy-three participants were assigned to high-, medium-, and low-proficiency groups. Three major instruments were administered, a background questionnaire, the Questionnaire of English Self-Efficacy, and the Questionnaire of English Self-Regulated Learning Strategies. The results reveal that there were significant differences among groups in terms of self-efficacy beliefs for listening, speaking, reading, and writing, showing that high-proficiency learners held a higher sense of self-efficacy than medium- and low-proficiency learners. The study also indicates that there were significant differences among groups when looking at self-regulated learning strategy use. Successful learners employed more self-regulatory skills than others. Additionally, a positive correlation was found between self-efficacy and self-regulation. Based on the results, pedagogical implications are suggested.