Objective To evaluate the efficacy of probiotics for treating irritable bowel syndrome (IBS). Methods The following databases as PubMed, The Cochrane Library, Web of Science, EMbase, MD Consult, CNKI, CBM and WanFang Data were searched from the data of their establishment to June 2011 to collect the randomized controlled trials (RCTs) on probiotics for treating IBS. The data were extracted and cross-checked independently by two reviewers, the methodological quality of trials was evaluated with Cochrane Handbook 5.0.2 criteria, and Meta-analysis was conducted using RevMan 5.1 software. Results A total of 20 RCTs involving 1 713 patients were included. Results of meta-analyses showed that compared with the placebo, probiotics was statistically and significantly better in improving the overall symptoms, alleviating abdominal pain/discomfort and relieving abdominal distention. Conlusion Current evidence shows probiotics may play a role in improving the symptoms of IBS. Due to a lot of differences existing among the included studies in aspects of methodological quality, diagnostic criteria, evaluation methods, dosage and course of treatment, this conclusion should be further tested with more strictly-designed and high-quality RCTs.