Abstract: Objective To investigate the relationship between small intestinal bacterial overgrowth (SIBO) and irritable bowel syndrome (IBS) and look for new ideas for the pathogenesis and treatment of irritable bowel syndrome. Methods From January 2013 to January 2015, 120 IBS patients in our hospital were chosen as observation group, 60 healthy volunteers in physical examination center in our hospital at the same period were selected as control group. Patients in two groups underwent lactose methane-hydrogen breath test, inflammatory cytokines detection and IBS symptoms integral questionnaire. IBS patients with SIBO positive were treated for 2 weeks by rifaximin capsule, then they received methane-hydrogen breath test. IBS patients with SIBO positive were divided into SIBO turning-negative group and not turning- negative group according to the Results of hydrogen breath test and the treatment efficacy were observed. Results The SIBO positive rate between observation group and control group (68.33% vs 18.33 %) had statistical differences (P< 0.005); The turning-negative rate of rifaximin capsule was 70.73%; After treatment, IBS symptoms score and inflammatory cytokines in both SIBO turning-negative group (symptoms score: 3.96±1.42 vs 12.45±3.78; IL-6: 97.32± 13.83 vs 158.84±15.51; TNF-α: 29.67±6.19 vs 42.67±7.65) and not turning- negative group (symptoms score: 7.89±2.37 vs 12.39±3.69; IL-6: 126.79±14.29 vs 156.43±15.49; TNF-α: 35.12±6.67 vs 43.27±7.64) were significantly lower than before (P< 0.05); IBS symptoms score (3.96±1.42 vs 7.89±2.37), inflammatory cytokines (IL-6: 97.32±13. 83 vs 126.79±14.29; TNF-α: 29.67±6.19 vs 35.12±6.67) and treatment efficacy (82.75% vs 62.50%) in SIBO turning-negative group were superior to not turning- negative group (P< 0.05). Conclusion There is a high incidence of SIBO in patients with IBS. Treating SIBO can improve the clinical symptoms of patients with IBS.