Objective To study the mechanism of Sanhuang Decotion in the treatment of ulcerative colitis(UC)under Candida albicans colonization in mice based on Dectin-1-Syk-CARD9 signaling pathway.Methods Mice model of UC with fungal colonization were established with dextran sodium sulfate free drinking and C.albicans intragastric administration.Mice were divided into normal control group,model group,sulfasalazine group,fluconazole group,and Sanhuang Decotion low-and high-dosage groups,and receive corresponding drug interventions.General state of mice were observed,and the disease activity index(DAI)score of mice were calculated.The load of C.albicans in intestine was detected,the length of the colon was measured,and pathological scoring of the colon tissue was performed.The ultrastructural changes of colon epithelium were observed under transmission electron microscopy.The contents of TNF-α,IL-6 and IL-12 in serum and colon tissues were detected by ELISA.The mRNA and protein expression of Dectin-1,Syk,CARD9,NF-κBp65 and inflammation factors in intestinal epithelial cells and colon tissues were detected by qPCR,Western blot and immunohistochemistry.Results Compared with the normal control group,the model group mice showed reduced activity,decreased food intake,accompanied by loose stools,significantly increased DAI score,increased load of C.albicans in the intestine,shortened colon length,and increased histopathological score,with widening of gap between colon epithelial cells,cytoplasmic dissolution,mitochondrial swelling;TNF-α,IL-6 and IL-12 in serum and colon tissue increased,the expressions of Dectin-1 and CARD9 mRNA and protein in colon epithelial cells increased,p-Syk,p-NF-κBp65,CARD9,TNF-α,IL-1β,IL-6 protein expression in colon tissue increased(P<0.01,P<0.05).Compared with the model group,the Sanhuang Decotion high-dosage group mice showed a significant decrease in DAI score,decreased intestinal C.albicans load,increased colon length,decreased histopathological score,more complete and orderly arrangement of microvilli in colon epithelial cells,mild mitochondrial swelling,TNF-α,IL-6 and IL-12 in serum and colon tissue decreased,and the mRNA and protein expression of Dectin-1 and CARD9 in colon tissue increased,the expression of p-Syk,p-NF-κBp65,CARD9,TNF-α,IL-1β,IL-6 protein in colon tissue decreased(P<0.01,P<0.05).Conclusion Sanhuang Decotion may exert an anti C.albicans colonization UC effect by inhibiting the Dectin-1-Syk-CARD9 signaling pathway and reducing the release of inflammatory factors.