The current systematic literature review intends to obtain a comprehensive understanding of the effect of computer-mediated peer written feedback on adult English as a second language (ESL)/English as a foreign language (EFL) writing through a systematic synthesis of primary peer-reviewed studies published from 2000 to 2016. Using a Grounded Theory approach, the included 12 studies were carefully reviewed and coded in a theme-based coding system by the authors. This review summarized information on research design, results, discussions, and limitations extracted from the included studies. The findings confirmed the conclusion from previous research syntheses on the effect of peer feedback and CMC in second language acquisition (SLA; Chen, 2016; Lin, 2015) and acknowledged the positive impact of computer-mediated peer written feedback on adult ESL/EFL writing. However, factors that could fluctuate the effect of this approach were also identified, including CMC technology, types and content of peer feedback, learners' language proficiency and technology anxiety. Based on the findings, this review further proposed a) research needs in the areas of peer feedback in SLA and b) implications for ESL/EFL teachers to effectively employ computer-mediated peer written feedback as an instructional strategy in writing classrooms.