Primary sclerosing cholangitis (PSC) is a chronic cholestatic disease characterized by inflammation and fibrosis of the bile ducts. Cholestasis may lead to hepatic inflammation and fibrosis, and amelioration of cholestasis may allow recovery from inflammatory and fibrotic pathological damage.Prevotella copri(P. copri) interventions have been reported to significantly improve cholestasis and liver fibrosis in 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC)-induced PSC mouse models. Even thoughP. copritreatment alone cannot bring about recovery from DDC-induced inflammation, it increases the abundance ofLactobacillus murinus(L. murinus) compared with DDC treatment, which has been reported to have anti-inflammatory effects. The abundance of L. murinus still not recovering to a normal level may underlie hepatic inflammation inP. copri+ DDC mice. Separate or combined interventions ofP. copriandL. murinuswere used to investigate the molecular mechanism underlying the improvement in PSC inflammation and fibrosis.P. copriandL. murinussignificantly reduced the hepatic inflammatory cell aggregation and inflammatory factor expression as well as the hepatic collagen content and fibrin factor expression in the PSC mice. Further analysis of phosphorylation and dephosphorylation levels revealed that treating the PSC mice with theP. copriandL. murinuscombined intervention inhibited the activity of the DDC-activated TGF-β1/Smad pathway, thereby reducing liver inflammation and fibrosis. The combination ofP. copriandL. murinusinhibits the TGF-β1/Smad pathway and reduces inflammation and fibrosis in PSC.