Objective To systematically assess the efficacy and safety of probiotics in prevention and treatment of bronchial asthma. Methods Randomized controlled trials (RCTs) of probiotics in prevention/treatment of asthma compared with placebo were searched in PubMed, EMbase, Web of Science, OVID and The Cochrane Library published before August 2011. The quality of the included RCTs was evaluated and the data were extracted by two assessors independently. Meta-analyses were performed with RevMan 5.1 software. Results Eleven RCTs on probiotics preventing asthma (n=3 656) and 5 RCTs on probiotics treating asthma (n=430) were identified. The Meta-analyses on preventing asthma showed that probiotics didn’t statistically decease the incidence of asthma (RR=0.76, 95%CI 0.47 to 1.22, P=0.25) and asthma-like wheezing (RR=0.92, 95%CI 0.62 to 1.39, P=0.71) compared with placebo. The Meta-analyses on treating asthma indicated that probiotics could prolong free episodes of asthma (RR=1.48, 95%CI 1.20 to 1.76, Plt;0.000 1) in comparison with placebo. No severe adverse events were found in all included studies. Conclusion The present evidence is not b enough to prove that probiotics is effective to prevent asthma, but it may prolong free episodes of asthma. Although it seems to have the effect on improving lung function, it fails to reduce the acute onset of asthma and has no have the advantage of improving immune function.