Abstarct: Although the effect of traditional modes of practice has been tested, the effect of deliberate practice has not been tested. To fill this gap, this study aims at testing the effect of deliberate practice on EFL learners’ oral proficiency. The experimenter utilized a sample consisting of 120 Iranian EFL learners studying English at the intermediate level. Individual pre-test and post-test measures were conducted in consonance with the randomized Solomon four-group design. Groups of learners were randomly assigned to one of the four experimental and control groups. The experimental group was instructed through deliberate practice while control group received mechanical practice. Post-test scores were analyzed by 2×2 analysis of variance (ANOVA). It was found that deliberate practice significantly affects learners` oral proficiency, F (1,116) = 74.51, p ˂0 /005. It was also found that pre-test does not affect the results of the study, F (1,116) = 1.83, p=0 /17 and F (1,116) = 0/047, p=0 /83. The findings of the study have clear implication for both language learners and language teachers.