This study investigated the effects of metacognitive instruction in oral communication for EFL learners over a semester. Participants (N = 58) were sampled from four oral communication classes in a private university in the western part of Japan where the researcher had been working as an English instructor. They were freshmen whose majors were not English. The treatment group (n = 28) received metacognitive instruction in oral communication (i.e., they were taught how to improve oral communication skills and how to become more autonomous learners through metacognitive processes as well as activities such as planning, monitoring, and reflecting). The contrast group (n = 30), taught by the same teacher, did not receive metacognitive instruction although they used the same textbooks and materials and had more time for interaction in English. Results of the questionnaire (SRLQ, the Self-Regulated Learning in Oral Communication Questionnaire, Kobayashi, 2016a) showed that students in the treatment group became more self-regulated learners. Moreover, it was found that the treatment group made greater gains in interactional competence, regulation of cognition, cognitive strategies and interaction strategies. Furthermore, it was verified that learners with low interactional competence in the treatment group benefited the most from such metacognitive instruction.