Flipped classroom is a pedagogical approach that inverts the flow of the traditional classroom. Due to recent interest in the effectiveness of the flipped learning, research on flipped learning has become pervasive. The purpose of this study, therefore, is to explore the applicability of flipped learning approach to the teaching of English vocabulary for Korean EFL learners. The participants of the study were 40 Korean high school students in Seoul and they were divided into two groups (flipped classroom and traditional classroom). The major results and findings of the study are as follows: The flipped classroom promoted the vocabulary acquisition of Korean high school students in terms of receptive and productive knowledge, which was shown to have a long-term effect. In addition, the flipped classroom had a positive effect on students’ learning attitudes and self-directed learning. Furthermore, the participants’ perceptions of the flipped classroom were very positive. Thus, the implementation of flipped learning will enable Korean instructors not only to explicitly teach vocabulary but also to encourage self-directed and interactive learning to take place in class. Given the beneficial effects of flipped classroom on the vocabulary learning, there is a need for further investigation of the flipped classroom on various skills of English.