This study explores motivation and self-regulatory capacity of Korean high school students when they are learning English vocabulary and compares those to their English competence. A total of 127 learners were assigned to advanced, intermediate, or lower groups based on their English vocabulary knowledge. Four instruments were employed: a background questionnaire, a Vocabulary Levels Test, the English Vocabulary Learning Motivation (EVLM) scale, and the Self-regulatory Capacity in English Vocabulary Learning (SCEVL) scale. Results show that advanced and intermediate learners exhibited significantly higher outcomes than those in the lower group in intrinsic motivation, identified regulation, and external regulation on the EVLM. Advanced learners also had significantly greater outcomes than those in the lower group in commitment, metacognition, satiation, emotion, and environment control on the SCEVL. Significant correlations were found among vocabulary knowledge, motivation, and self-regulation in English vocabulary learning. Pedagogical implications and practical methods are suggested for English teachers to help better facilitate their students’ vocabulary competence and affective growth.