This meta-analysis reports the results of a systematic synthesis of primary studies on the effectiveness of computer-mediated communication (CMC) in second language acquisition (SLA) for the period 2000-2012. By extracting information on 21 features from each primary study, this meta-analysis intends to summarize the CMC research literature for the past decade by calculating an average effect size and performing a series of moderator analyses to factor out elements that might mediate the effect of such media in SLA. In total, 59 studies were identified as eligible after excluding three outlier studies, covering both published and unpublished studies. All studies were coded for learner characteristics (5 features), methodological characteristics (14 features) and publication characteristics (2 features), six of which were further analyzed as moderator variables. The results show that (a) there was a positive and medium overall effect for CMC used for instructional/learning purposes in SLA, (b) among the four language skills which CMC was intended to facilitate, writing skills produced the largest effect size, as did pragmatic competence, among the three language components, i.e. pragmatics, vocabulary and pronunciation explored in this meta-analysis; however this result should be interpreted as tentative since only one study measured pragmatic competence in the current meta-analysis, and (c) smaller group studies produced a larger effect size than those using larger groups or no grouping.