Based on the establishment of the ulcerative colitis mice model induced by dextran sulphate sodium （DSS）， this study explored the protective effect of antimicrobial peptide LL-37 on the intestinal mucosal barrier of mice. Forty-eight male C57BL/6 mice were randomly divided into four groups： control group（drinking normal water）， DSS group （drinking 3% DSS water）， DL group （drinking 3% DSS water and administrating LL-37 by intraperitoneal injection） and LL group （administrating LL-37 by intraperitoneal injection）. The experiment lasted for 8 days， during which the disease activity index of mice was evaluated. Immunohistochemistry was used to analyze the degree of inflammatory infiltration of immune cells. Intestinal permeability was detected by ELISA and Ussing chamber. The secretion of inflammatory cytokines was analyzed by ELISA. Real time PCR was used to analyze the expression level of tight junction proteins in colon. The results showed that LL-37 （5 mg/kg·d） could obviously alleviate colitis symptoms such as weight loss， diarrhea and intestinal bleeding in mice， reduce disease activity index of mice. At the same time， LL-37 significantly improved the colonic morphology destruction， inflammatory cell infiltration， and the secretion of inflammatory cytokines TNF-α， IL-1β and IL-6 in serum of mice with colitis （P<0.05）， LL-37 also alleviated the decreased mRNA expression level of the three tight junction proteins in colon （P<0.05） and increased permeability （P<0.05）. These results revealed that LL-37 may alleviate the increase of intestinal mucosa permeability in mice with colitis by reducing the secretion of inflammatory cytokines in colon tissue and enhancing the expression of tight junction proteins， so as to realize the protective effect on the intestinal mucosa barrier in mice.