Our result showed that the expressions of epithelial cell tight junction proteins claudin-1, occludin, and ZO-1 were reduced remarkably in DSS-induced colitis in vivo and in TNF-α-induced cell injury model in vitro, while after the administration of formononetin, we found that formononetin increased the expressions of claudin-1, occludin, and ZO-1 significantly, suggesting that formononetin could protect the colonic mucosal integrity and maintain the colonic epithelial barrier function of colitis. This evidence concerns the gene CLDN1 and colitis.