Abstarct: Integrated skills approach as a way of teaching language in which language skills are incorporated and interwoven with each other during teaching has become a dominant trend in language teaching. The goal of this research was to compute the overall effect size of integrated skills approach (ISA) as well as the sources and extent of variance in observed effects. To this end, the study carried out a mexta-analysis of the effects of integrated skills approach on learners’ language proficiency in which 22 experimental and quasi-experimental studies from peer-reviewed journals published from 1983 to 2019 of and 46 effect sizes were reviewed and synthesized. Results indicated an overall effect size of 1.18 demonstrating a strong effect size. Also, the effect sizes of moderator variables were calculated and it was reported that the integrated skills approach has the most effect in advanced learners and university level. These findings indicate that although they might improve their main language skills, vocabulary and grammar are not influenced significantly. The findings of this mexta-analysis have implications for EFL/ESL teachers, researchers, policymakers and curriculum developers.