This study is aimed to explore the protective effects and mechanism of Sanguisorbae Radix (SR) in treating acute ulcerative colitis (UC) from the perspective of gut microbiota.Rats were divided into control group,UC model group,SR low dosage and high dosage group.Acute UC model was induced by 3.5% DSS for 7 days,and then the extract of SR was given to rats by intragastric administration.After 7 days of intervention,the body weight and DAI score of rats were recorded,pathological changes of colon tissue were observed by HE staining,contents of inflammatory factors were detected by ELISA,and the changes of gut microbiota in rats feces were detected by high-throughput sequencing technology.The results showed that SR could alleviate the weight loss and reduce the DAI score of UC rats (P<0.05);protect the morphological integrity of colon tissue and improve the colonic mucosal injury in UC rats;reduce the level of IL-6,IL-1β and TNF-α in the serum and colon of rats (P<0.05).SR could regulate the gut microbiota diversity significantly and restore the balance of intestinal bacteria.The results indicated that SR might repair the colonic mucosal injury by regulating the gut microbiota of UC rats,which could play a positive role in UC treating.