Objective To explore whether aging increases severity of colitis in mice and its mechanism.Methods Young (6-8 weeks)and aged (56 weeks) C57Bl/6 mice were divided into the control and experimental group (n=5,each). Dextran sodium sulfate(DSS) was used to induce acute colitis mouse model in the experimental group.The mRNA expressions of tumor necrosis factor-α(TNF-α)and interleukin-6(IL-6)in colon were measured by RT-PCR. Tight junctions (TJs) of intestinal epithelial cells was examined by transmission electron microscopy (TEM). Protein expressions of E-cadherin and occludin were detected by Western blotting and immunohistochemistry in colon.Results Compared with the young DSS-induced mice,the aged DSS-induced mice had more weight loss(t=3.679,P=0.006),higher disease indexes (t=2.496,P=0.037),higher histologic scores(U=0.000,P=0.008) and higher colonic IL-6 level (U=4.000,P=0.191). The TJs of intestinal epithelial cells were discontinuous in old healthy rats,and the TJs were destroyed significantly in both young and aged DSS-induced mice. Compared with the young DSS-induced mice,the aged DSS-induced mice had decreased protein expressions of E-cadherin (t=0.184,P=0.863)and occludin (t=0.399,P=0.710).Conclusions Aging leads to more severe disease following DSS challenge. Age-related deterioration in the functions of the gastrointestinal barrier and integrity may be one of the possible mechanisms.