Abstract: Objective To explore the effect and mechanism of probiotic in treatment of constipation induced by loperamide in ICR mice. Methods 30 ICR mice were randomly divided into three groups: normal group, constipation group, probiotic group , 5 mg·kg-1 of loperamide was given intraperitoneally to constipation group and probiotic group for 7 days to establish the models of constipation. Then the probiotic group were given probiotic 10 mg·kg-1 daily by gavage, for 14 consecutive days. Mice in the normal group, constipation group received an equal volume of saline for 14 consecutive days. At Day 14, the fecal parameters and small intestinal transit were detected. The expression of bcl-2 and bax were determined by Western blotting analysis. Results Compared with the normal group, the fecal pellets, fecal water content, intestinal transit ratio and bcl-2 protein expression decreased in constipation group (P < 0.05),but bax protein expression was significantly increased (P < 0.05); Compared with the constipation group, the fecal pellets, fecal water content, intestinal transit ratio and bax protein expression were significantly reduced in the probiotic group (P < 0.05), but bcl-2 protein expression was significantly increased (P < 0.05). Meanwhile the histological parameters were also improved in the probiotic groups. Conclusion Probiotics can significantly relieve the symptoms of constipation and histological parameters in mice by regulating bcl-2 and bax protein expression ratio