Purpose: To investigate the alleviating effects of three grapefruit peel pectins extracted by alkali (P10)， cellulase (C)， and alkali + cellulase (P10+C)， on dextran sodium sulfate-induced acute colitis of the mice. Methods: The mice were randomly divided into normal group， model group， P10 group， C group and P10+C group. The changes of tissue structure， inflammatory factors， gut microbiota and short-chain fatty acids were analyzed by staining， ELISA， 16S sequencing and gas chromatography， respectively. Results: The alleviating effects were most significant for P10+C， followed by P10 and C. P10+C significantly reduced disease activity index and spleen hypertrophy in DSS induced colitis mice， alleviated colon shortening and redness， colonic mucosa damage， crypt destruction and goblet cell reduction， and effectively protected the intestinal barrier. P10+C significantly increased the levels of anti-inflammatory cytokines (IL-10) and inhibited the secretion of pro-inflammatory cytokines (IL-6， IL-1β， TNF-α). Meanwhile， P10+C improved the richness and diversity of gut microbiota of colitis mice， increased the relative abundance of beneficial bacteria Akkermansia， Clostridium_sensu_stricto_1， Lachnospiraceae_NK4A136_group， Lactobacillus， and Ruminococcaceae_UCG-014， and promoted the production of short chain fatty acids， thus alleviating intestinal inflammation. Conclusion: P10+C can be used as a potential prebiotic to alleviate acute colitis.