Abstract: Houttuynia cordata is traditionally used as phytoantibiotics for treating lung disease in China. Houttuynia cordata polysaccharides (HCPs) have been reported to alleviate influenza virus-induced intestinal and lung immune injury by regulating the gut-lung axis. The present study aims to investigate the effects and mechanisms of HCPs on ulcerative colitis (UC). Male C57BL/6 mice were induced by dextran sodium sulfate (DSS) to establish the UC animal model. Our results showed that HCPs significantly reduced the weight loss and the shortening of colon length in colitis mice, and relieved the pathological damage of colon mucosa and inhibited the expression of pro-inflammatory cytokines such as TNF-α, IL-1β, IL-6, etc. It was suggested that HCPs could significantly improve DSS-induced colitis in mice. HCPs directly protected intestinal epithelial cells, ameliorated epithelial barrier dysfunction and cell apoptosis, which was also proved in H₂O₂ stimulated cell apoptosis model. HCPs inhibited inflammation in the colon, which was related to suppressing the infiltration of macrophages, inhibiting the expression of pro-inflammatory cytokines and proteins (TLR4, NF-κB), and restoring the dysfunction of Th17 and Treg cells. HCPs also restored the alteration of intestinal flora induced by DSS, increased the abundance of Firmicutes and Bacteroides, and reduced the abundance of Proteobacteria. This study confirmed the protective effect of Houttuynia cordata polysaccharide extracted from traditional Chinese medicine on ulcerative colitis, of which the mechanism was closely related to the maintenance of intestinal homeostasis (intestinal barrier , immune cells , and intestinal bacteria).