Understanding the beliefs held by the learners about learning a language, and the way they utilize their thoughts about knowledge and learning seem essential for planning a constructive language program. Following this line of research, this paper aims at testing a hypothetical model of the relationship between epistemic beliefs (EBs) and subscales of language-learning strategies (LLSs) through the mediating role of learners’ self-efficacy (LSE). To this end, a sample of 300 Iranian high school students, taking regular courses, completed three survey questionnaires. At this stage, correlational analysis and structural equation modeling (SEM) were employed to probe the interconnections, analyze the model, and outline the conceptual framework. The results revealed that the LSE framework can adequately account for the learners’ LLSs. In particular, the results indicated that efforts, persistence, and imitation (i.e., the subfactors of LSE) positively and significantly influenced LLSs. However, EBs with the mediating role of LSE were known to be a significant factor in demoting the LLSs. Notably, knowledge and learning agents were the negative predictors of LLSs. This paper suggests that LSE has higher explanatory power than EBs in predicting LLSs. The findings of this study suggest that teachers and material developers should pay serious attention to the learners’ self-efficacy as they were known to influence LLSs.