Objective To assess the clinical effectiveness of vacuum-formed versus Hawley retainers in the period of retention. Methods PubMed, The Cochrane Library, EMbase, CBM, CNKI, VIP, and WanFang Data were searched from the date of their establishment to December 31, 2011, to collect the randomized controlled trials (RCTs) about the clinical effectiveness of vacuum-formed versus Hawley retainers. The quality of the included studies was evaluated by two reviewers independently, and meta-analysis was performed by using RevMan 5.1.4 software. Results Six RCTs including 935 patients were identified. The results of meta-analyses showed significantly fewer changes in irregularity of the maxillary incisors (MD=0.13, 95%CI 0.04 to 0.21) and mandibular incisors (MD=0.29, 95%CI 0.24 to 0.33) in the vacuum-formed group than in the Hawley group. There were no significant differences between the two groups in maxillary intercanine width (MD=?–0.01, 95%CI –0.03 to 0.01), mandibular intercanine width (MD=0.04, 95%CI –0.02 to 0.10), maxillary intermolar width (MD=?–0.01, 95%CI –0.03 to 0.00) and mandibular intermolar width (MD=?–0.02, 95%CI –0.08 to 0.04). The results of qualitative analysis were consistent with the results of meta-analysis and there were no significant differences in overjet and overbite. Conclusion Vacuum-formed retainers are more effective than Hawley retainers at maintaining position of incisors in the period of retention. In other aspects, they are similar. In consideration of the factors such as the limited quality and incomplete measure index of primary studies, RCTs of higher methodological quality are needed.