This article examines the relationship between the English medium instruction teacher's classroom leadership and their teaching self-efficacy. The self-reported data were collected from 188 English-medium instruction teachers at a Chinese public university. The correlational analysis of data revealed that there was a close positive relationship between "classroom leadership" and "teaching self-efficacy" (r = 0.70, p < 0.001), and the teacher's classroom leadership contributed 48% of the variance of their teaching self-efficacy. Among the three components of teaching self-efficacy, "self-efficacy for student engagement" had the highest correlation with the teacher's classroom leadership (r = 0.66, p < 0.01). The multiple regression analysis showed that "teaching self-efficacy" was significantly predicted by two components of classroom leadership, that is, "intellectual stimulation" ([beta] = 0.29, p < 0.001) and "idealized influence" ([beta] = 0.24, p < 0.05). The ANOVA test results showed that classroom leadership increases with the teacher's EMI teaching experience, reaching the highest when it gets to 10 years, and then decreases later, while teaching self-efficacy increases continuously. The findings have great potential to open new areas for the development of the English-medium instruction teacher's self-efficacy.