The primary purpose of this study was to ascertain whether the degree to which Korean middle school students perceived their teachers to be credible made a difference in the effectiveness of teachers' persuasion as a source of students' academic self-efficacy. In the contexts of both general school learning and a specific subject of Korean language and literature, social persuasions by teachers were a significant predictor of student self-efficacy. Students' academic self-efficacy, in turn, was a significant predictor of students' expected final examination scores. Although perceived teacher credibility did not predict student self-efficacy directly, it interacted significantly with teacher persuasion in the prediction of student self-efficacy, as determined by the latent interaction analysis. Consistent with Bandura's assertion and our hypothesis, students reported stronger academic self-efficacy as they perceived the teachers who delivered the social persuasion to be more credible.