Researchers in education have documented that teachers' sense of efficacy has strong impacts on various aspects of teaching and learning. Yet, in the field of TESOL, inquiry into teachers' sense of efficacy is extremely scarce. The present study, by adopting the notion of teachers' sense of efficacy as the theoretical framework, has explored Iranian English Institute teachers' confidence in teaching English. The study has also examined teachers' attitudes toward the English language and teachers' English language proficiency, respectively. An exploratory survey methods design was employed in the present study and data were collected in the quantitative format, by which 68 English institute teachers working in Mazandaran responded to the survey. The results indicated that teachers' current level of English proficiency and EIL (English as an International Language) attitude toward the English language were the significant predictors for teachers' English teaching-specific efficacy beliefs or confidence. Also, efficacy for oral English language use was found as an additional dimension of teacher efficacy in teaching English, indicating that in a foreign language context, oral target language use would be a significant dimension to be considered in examining teachers' self-efficacy in teaching the target language.