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 mixed-method 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.