Recently, Japanese medical students are expected to acquire a high degree of English proficiency with the tacit understanding that it will feature in their future profession through interactions with non-Japanese patients and/or engagement with medical research. However, to the best of our knowledge, the motivation of Japanese medical students to learn English as a second language (L2) has not been studied. Using quantitative and qualitative questionnaires, we investigated the L2 learning motivation of second-year Japanese medical students and the degree to which the students have international posture, i.e., their awareness and openness to internationalization. The results revealed that the students were primarily instrumentally and vocationally motivated; in other words, their chief motivation for L2 learning came from an understanding of the usefulness of L2 proficiency for their future profession. The results also showed that the students had strong international posture, as evidenced by a deep desire to communicate internationally and an understanding of the role of English as a tool for global communication. The findings suggest that, to sustain or improve L2 learning motivation, educators should employ study materials that are pertinent to students' future needs and professions.