BACKGROUND AND AIMS Crohn's disease is an autoimmune disease associated with imbalanced mucosal immunity, mediated with increased Th1 and Th17 cells. Laquinimod, an immunomodulatory drug, has shown efficacy in regulating the differentiation of T cells. The aim of the study was to investigate the therapeutic effect of laquinimod on spontaneous colitis in interleukin-10-gene-deficient mice, an animal model of Crohn's disease. METHODS Male Il10(-/-) mice aged 16weeks in the laquinimod group were treated with laquinimod with distilled water at a dose of 25mg/kg by oral gavage, 3 times a week. Il10(-/-) mice in the IL-10-KO group and wild type mice received equal volume of phosphate buffered saline by oral gavage, 3 times a week. After 4weeks, mice were sacrificed for analysis. Severity of colitis, epithelial expression of T-cell-associated cytokines, expression and distribution of tight junction proteins in the lamina propria and NF-κB signaling pathway associated mRNA expression were measured at the end of the experiment. RESULTS Laquinimod treatment ameliorated spontaneous colitis in Il10(-/-) mice, which was associated with decreased T-cell-associated pro-inflammatory cytokines. Increased expression and correct distribution of tight junction proteins (occludin and ZO-1) were found in Il10(-/-) mice treated with laquinimod. In addition, in mice treated with laquinimod, NF-κB signaling pathway associated mRNA in the colon was also downregulated. CONCLUSIONS Our results indicated that laquinimod treatment ameliorates colitis in Il10(-/-) mice and improves intestinal barrier function, which may support a new therapeutic approach to Crohn's disease.