Pectin as a dietary fiber supplement has shown emerging potential in clinical ulcerative colitis (UC) adjuvant therapy. In this study, the preventive and prebiotic effects of enzymatically degraded pectic oligosaccharides (POS) were further explored in dextran sodium sulfate (DSS)-induced colitis mice. The POS supplement (400 mg kg-1) was significantly effective at improving preventive efficacy, promoting colonic epithelial barrier integrity and reducing inflammatory cytokines. Meanwhile, the changes in T regulatory (Treg) cells and T helper 17 (Th17) cells indicated that POS treatment regulated the Treg/Th17 balance. Gut microbiota analysis showed that the POS supplement reshaped the dysfunctional gut microbiota. Further Spearman's correlation coefficient analysis indicated that the changes of the gut microbiota were highly associated with modulating the epithelial barrier, promoting the development of Treg cells and suppressing the differentiation of pro-inflammatory Th17 cells. All of these results suggest that enzymatically- degraded POS is a promising therapeutic agent for UC prevention and adjuvant treatment by maintaining intestinal homeostasis.