It has been noticed that gastroenteritis or dysentery plays a role in pathogenesis of irritable bowel syndrome (IBS), and antibiotics can increase functional abdominal symptoms, both of which may be partly due to intestinal flora disorders. This study was to determine the change of gut flora of IBS, a cluster of abdominal symptoms. Because of the chronic course and frequent occurrence of the disease, IBS patients suffered much from it. So the quality of life (Qol) of IBS patients was also evaluated in this study. Twenty-five Rome II criteria-positive IBS patients were recruited, and 25 age and gender-matched healthy volunteers were accepted as control. The fecal flora, including Lactobacillus, Bifidobacterium, Bacteroides, C. perfringens Enterobacteriacea and Enterococus, were analyzed quantitatively and qualitatively. We also calculated the ratio of Bifidobacterium to Enterobacteriaceae (B/E ratio) in both IBS patients and controls. In both groups, the data were further analyzed based on age difference, and comparisons were made between the younger and elder subgroups. We also evaluated the quality of life (QoL) of IBS patients and the control group using the Chinese version of SF-36 health questionnaire. In IBS patients, the number of fecal Bifidobacterium was significantly decreased and that of Enterobacteriaceae was significantly increased compared with that in healthy controls (both P<0.05). The mean microbial colonization resistance (CR) of the bowel in IBS patients was smaller than 1, making a significant difference compared with that in control which was more than 1 (P<0.01). There was no significant difference in gut flora between two subgroups. While in control, the elder subgroup presented more Enterobacteriacea than the younger one (P<0.05). Compared with the control group, IBS patients had significantly lower scores on all SF-36 scales, with the exception of physical functioning. However, there was no significant correlation between quality of life and enteric symptoms in IBS patients. There are intestinal flora disorders in IBS patients, which may be involved in triggering the IBS-like symptoms. IBS patients experience significant impairment in QoL, however, the impairment is not caused directly by enteric symptoms.