Abstract: In this study,we used Bletilla striata polysaccharide (BSP) to treat the UC mice induced by oxazolone and study the efficacy and possible mechanism of BSP treatment on UC mice model.The animal experiment results showed that the murine UC models could be successfully induced by oxazolone.After the administration of BSP on the murine UC models,murine colitis was significantly suppressed,colon mucosal regeneration was promoted and Th2 related immune response was inhibited.Therefore,it was proved that BSP had significant effects on UC.In vitro experiments further demonstrated that BSP might inhibit lymphocyte activation and secretion of related cytokines via suppressing the activity of macrophages,which indicated BSP has immunoregulation activity.