Objective: Compound sophorae decoction, a Chinese medicinal formulae composed of six Chinese herbs, is effective for the clinical treatment of ulcerative colitis (UC). Some of its effective monomers had been proven to have suppressive effect on UC models. The aim of this study is to further explore the mechanism whether compound sophorae decoction ameliorates dextran sodium sulfate (DSS)-induced mice colitis by regulating the balance between T helper (Th) 17 and regulatory T (Treg) cells. Methods: Experimental model of UC, established by drinking water with DSS, was treated with compound sophorae decoction and mesalazine. The stool, activity, body weight of the mice, colon length and colon histopathology were observed to evaluate severity of colitis. The concentration of cytokines in colonic tissues were detected by ELISA. The expression of phosphorylated nuclear factor-kappaB (NF-kappa B) p65, STAT3 and phosphorylated STAT3 in colonic tissues were determined by western blotting and immunohistochemistry. The percentage of Th17 and Treg cells in spleen and mesenteric lymph nodes (MLNs) were detected by flow cytometry. The levels of transcription factor ROR-gamma t and FOXP3 in colon tissues were detected by qRT-PCR and immunohistochemistry. Results: The aqueous extract of compound sophorae decoction was able to improve the symptoms and pathological damage of mice. The body weight of mice were increased and DAI were significantly decreased; ulcers were slighter than DSS group. The administration of compound sophorae decoction reduced the level of inflammatory factors interleukin (IL)-1 beta, tumor necrosis factor (TNF)-alpha and phospho-NF-kappa B p65, and also decreased the proportions of Th17 cells in spleen and MLNs and the expression of ROR-gamma t, IL-17A, STAT3, IL-6 in colonic tissues; while the percentage of Treg cells in spleen and MLNs and the expression of FOXP3, transforming growth factor (TGF)-beta 1, IL-10 in colonic tissues were upregulated. Conclusion: Overall, this study suggested that compound sophorae decoction significantly improves the symptoms and the pathological damage of mice with colitis and influences the immune function by regulating Th17/Treg cell balance in DSS-induced colitis in mice.