Self-efficacy, as one of the most influential perceptions the learners hold, has recently been at the center of investigation due to its fundamental role in every domain particularly in language learning. Yet, more research on self-efficacy and its underlying processes is reckoned to be necessary in order to explore how the learners can be assisted in their academic achievement by activating their self-efficacy judgmental system; and likewise fostering their mental capacities. On the other hand, reading comprehension deemed to be one of the most essential requirements to master in an EFL setting is also considered to be a laborious task. Hence, this experimental study aims to investigate the effect of self-efficacy enhancement via strategy instruction on the achievement of Iranian EFL learners in reading comprehension. 90 EFL learners in pre-intermediate level of a private institute in Tehran were selected as the research sample using quasi-experimental research design and assigned to one control and two experimental groups randomly. To answer the research questions, a self-efficacy questionnaire taken from Becker and Gable (2009) and one of PET Reading Proficiency Tests were administered to the learners in three groups both at pretest and posttest. Cognitive and metacognitive strategies selected from Oxford's Strategy Classification were instructed to two experimental groups; in the meantime, the control group was taught the readings with no instruction based on strategies. The results revealed that self-efficacy enhancement can significantly affect the learners' achievement in reading comprehension (p<.05).