OBJECTIVE：To investigate the effects of Guizhi ful ing capsules and its principal components （paeoniflorin， paeonol and amygdalin ）on the intestinal flora of primary dysmenorrhea model rats. METHODS ：Female SD rats were randomly divided into normal group ，model group ，capsule group（Guizhi fuling capsule ，1 000 mg/kg），paeoniflorin group （15.0 mg/kg）， paeonol group （10.3 mg/kg）and amygdalin group （12.1 mg/kg），with 6 rats in each group. Except for normal group ，other groups were given estradiol benzoate subcutaneously on the back of rats and oxytocin intraperitoneally to induce primary dysmenorrhea model. From the 4th day after subcutaneous injection of estradiol benzoate ，normal group was given constant volume of normal saline intragastrically ；model group was given constant volume of 0.5％CMC-Na solution intragastrically ；administration groups were given relevant medicine intragastrically ，once a day ，for consecutive 7 days. The writhing times and the contents of and MDA in uterus tissue of rats were determined ，and then com the contents of short-chain fatty acids （SCFAs）such as acetic acid，propionic acid ，butyric acid in colonic contents were detected by GC method. Using diver sity index as index ， Rep-PCR and Eric-PCR were used to evaluate the d iversity of intestinal flora in feces of rats. RESULTS ：Compared with normal group，the writhing times of rats were increased significantly in model group ；the contents of NO and MDA in uterus were increased significantly ，while the contents of acetic acid ，propionic acid and butyric acid in colonic contents and total content of SCFAs were decreased significantly （P＜0.05 or P＜0.01）；the number of DNA electrophoresis bands of intestinal flora was significantly reduced ，the brightness of most bands was significantly reduced ，and the diversity indexes （by Rep-PCR and Eric-PCR method ，hereinafter）1 h after administration were significantly reduced （P＜0.05 or P＜0.01）. Compared with model group，writhing times of rats were decreased significantly in capsule group ，paeoniflorin group and paeonol group ；the contents of NO in uterus of rats in capsule group and paeoniflorin group as well as the contents of MDA in capsule group ，paeoniflorin group and paeonol group were decreased significantly （P＜0.05 or P＜0.01）；the propionic acid content and total content of SCFAs in colon of rats in capsule group ，the contents of acetic acid ，propionic acid and butyric acid ，total content of SCFAs in paeoniflorin group as well as the contents of propionic acid and butyric acid ，total content of SCFAs in paeonol group were increased significantly；the content of isovaleric acid was decreased significantly in paeoniflorin group （P＜0.05 or P＜0.01）；DNA electrophoresis bands and its brightness of intestinal flora changed to different extents in administration groups ，and the diversity indexes of intestinal flora 1 h after administration were increased significantly in capsule group and paeoniflorin group ，while those indexes were decreased significantly in paeonol group and amygdalin group （P＜0.05 or P＜0.01）. CONCLUSIONS ：Guizhi fuling capsules can significantly reduce writhing times and the contents of NO and MDA in uterus of primary dysmenorrhea model rats. At the same time ，the capsules also can regulate SCFAs content in colonic contents and intestinal flora diversity of rats. The above effects may be related to paeoniflorin and paeonol in the capsules.