To investigate the effects of polysaccharides(sodium alginate and fucoidan) from marine Chinese medicines on dextran sulfate sodium(DSS)-induced ulcerative colitis(UC) in mice.Methods:RAW264.7 cells were treated with different concentrations of sodium alginate and fucoidan，and cell viability was measured by CCK-8 assay.RAW264.7 cells were activated by lipopolysaccharide(LPS).ELISA kits were used to determine the content of NO and interleukin-6(IL-6) in the cell supernatant.Twenty-five female mice were randomly divided into blank control group，model group，positive control group，sodium alginate group，and fucoidan group，with 5 mice in each group.Except the blank control group，each group was treated with DSS by gavage for 7 days to establish a US model，and then the positive control group，the sodium alginate group，and the fucoidan group were treated with postbiotics，sodium alginate，and fucoidan by gavage，respectively.Blood samples were collected from eyeballs for the detection of serum inflammatory mediators.At the same time，mice were sacrificed under anesthesia，and colon tissues were obtained for biochemical indexes determination and histopathological analysis.Results:Sodium alginate and fucoidan did not cause toxicity to RAW264.7 cells even at high concentrations.In the concentration range of 500 to 1 000 μg/mL，both sodium alginate and fucoidan inhibited the secretion of NO and IL-6 in RAW264.7 cells in a concentration-dependent manner，and the effect of fucoidan was significantly better than that of sodium alginate.For DSS-induced UC in mice，sodium alginate and fucoidan can improve the clinical symptoms of UC，restore the body weight of mice，and reduce the secretion levels of serum inflammatory mediators tumor necrosis factor-α(TNF-α) and IL-6.Conclusion:Fucoidan and sodium alginate can treat DSS-induced UC by inhibiting the release of inflammatory mediators in serum，and the therapeutic effect of fucoidan is better than that of sodium alginate.