Abstract: The purpose of this study was to systematically evaluate the effects of three plant-derived mannans, locust bean gum (LBG), guar gum (GG) and konjac flour (KGM), on colitis and intestinal microecology in mice. Mice were fed with feed containing 2% three different mannans, and dextran sulfate sodium (DSS) was used to induce colitis. The physiological indexes of mice in each group were measured and the intestinal microbiota was analyzed. The results demonstrated that three mannans ameliorated colitis symptoms in mice to varying degrees, with guar gum exhibiting the most significant effects. Compared to the model group, guar gum intervention increased colon length by 20.0% (P<0.01), reduced the immune index by 22.7% (P<0.01), and decreased the number of mice with severe bloody stools by 50%. Further analysis revealed that guar gum significantly decreased the levels of pro-inflammatory cytokines IL-6, IL-1β and TNF-α by 26.8% (P<0.05), 48.9% (P<0.001) and 60.0% (P<0.001) respectively. Conversely, the anti-inflammatory cytokine IL-10 increased by 33.3% (P<0.01). Additionally, guar gum markedly elevated the concentration of short-chain fatty acids (SCFAs), particularly butyrate (P<0.05). 16S microbial diversity sequencing revealed that the three mannans had different regulatory effects on the structure of intestinal flora. KGM had a positive effect on improving intestinal microecological diversity. Guar gum had a significant effect on regulating multiple operational taxonomic units (OTUs) of Norank_f_Muribaculaceae, Enterorhabdus, Ruminococcus and other genera. These OTUs were significantly correlated with inflammation-related indicators or genera they belonged to have been reported to be closely related to short-chain fatty acid production and colitis. This study revealed the potential value of guar gum in the prevention and adjuvant treatment of colitis and the effect of intestinal microecology regulation in this process, which will benefit on the development of related functional foods.