Background: Debate exists regarding to whether thiopurine therapy is as effective as 5-aminosalicylic (5-ASA, mesalazine) in inflammatory bowel disease (IBD). In this study, we aimed to review the efficacy of azathio-prine (AZA) and 6-mercaptopurine (6-MP) in inflammatory bowel disease (IBD), and to conduct a meta-analysis of randomized controlled trials to compare the efficacy and safety of AZA/6-MP and 5-ASA in IBD. Methods: Selection of studies: Randomized controlled trials comparing AZA/6-MP with 5-ASA was included in the meta-analysis. Search strategy: Electronic and manual. Study quality: Independently assessed by two reviewers. Data synthesis: By " inten-tion- to-treat". Results: Eight trials (572 IBD patients) were included in the meta-analysis. All trials stated random allocation and reported withdrawal and dropout. Most of the trials reported blind, allocation concealment, intention-to- treat analysis, the calculation of sample size. Six studies showed that AZA/6-MP had lower relapse rate than 5-ASA (RR: 0.72, 95% CI: 0.55-0.95). Three studies showed that AZA/6-MP had higher remission rate than 5-ASA (RR: 3.30, 95% CI: 1.80-6.05). Compared with 5-ASA, AZA/6-MP did not show significant differences for endoscopic recurrence rate and therapeutic failure rate. Compared with 5-ASA, AZA/6-MP did not increase adverse events (RR: 1.16, 95% CI: 0.87-1.55). Conclusion: All the eligible trials were of high methodological quality. Thiopurine drugs (AZA/6-MP) are more effective than 5-ASA for the treatment of IBD.