 Recent evidence suggests that a shift in the host-gut microbial relationship as seen in small intestinal bacterial overgrowth SIBO may contribute to the pathogenesis of IBS.Overgrowth of microbiota in the small intestine can cause excessive gas production and malabsorption with a variety of nonspecific symptoms, such as diarrhea, gas bloating, abdominal pain and constipation.Glucose GBT and lactulose LBT breath test have been proposed as simple, inexpensive and non-invasive diagnostic tools for detecting SIBO with respect to the gold standard the culture of intestinal aspirates. Many antibiotics have been proposed in the last years for SIBO eradication.Rifaximin is a rifamycin derivative with antibacterial activity caused by inhibition of bacterial synthesis of RNA and which is effective against both gram-positive and -negative bacteria, including aerobes and anaerobes.As 0.1 of its oral dose is absorbed, rifaximin administration is associated to a very low side-effect incidence. However,there are still no effective and reliable treatment for IBS,so we intend to explore the prevalence of SIBO in IBS-D patients and evaluate the efficacy of rifaximin for IBS-D in Chinese population. 