The current meta-synthesis study investigated the effective strategies for improving critical thinking ability among EFL/ESL learners, and the relationship between language learning skills and critical thinking ability. To achieve this aim, meta-synthesis was selected as the design of the study. Therefore, some databases were searched using the defined key terms, in order to select the related qualitative, quantitative, and mixedmethod studies. As a result, 550 articles were found, 43 articles of which were included in the final review. Using thematic analysis, the obtained data from these 43 articles were analyzed in 6 steps and then coded for each research question. Although no single method was proposed in this study as the best to improve critical thinking, it was indicated that a number of them together can be effective when properly implemented. It was shown that all 4 language skills can be improved by enhancing the level of critical thinking ability among EFL/ESL learners.
