The present study explored English as a foreign language (EFL) students' motivation and self-efficacy. This is accomplished by incorporating the ten subfactors of L2 motivational self-system namely; criterion measures, ideal L2 self, ought-to L2 self, family influence, instrumentality promotion, instrumentality prevention, attitudes towards learning English, attitudes towards L2 community, cultural interest, and integrativeness. The Persian version of L2 Motivational Self-system Questionnaire and the English version of Learners' Self-Efficacy Survey were used to collect the data. The results estimated via correlation and regression analyses revealed that there was a significant relationship between L2 motivation and L2 self-efficacy. In other words, all the ten sub-factors predicted L2 self-efficacy positively and significantly among which criterion measures, attitudes towards learning English, instrumentality promotion, and ideal L2 self were the most powerful predictors of L2 self-efficacy.