Objective: To investigate the impact of Bifidobacterium MIMBb75 on ulcerative colitis (UC) mice by regulating vasoactive intestinal peptide (VIP)/cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA) and mammalian target of rapamycin (mTOR) pathways. BALB/c mice were randomly separated into normal control (NC) group, colitis model (UC) group, Mesalazine group, MIMBb75 low and high dose groups, Methods: MIMBb75 high dose combined VIP antagonist group, and MIMBb75 high dose combined MHY1485 group (10 per group), except for the NC group, 5% dextran sodium sulfate (DSS) was applied to induce the UC model. After the treatment, the general condition and UC disease activity index (DAI) of the mice were observed, and then pathological injury of intestinal tissues, myeloperoxidase (MPO) activity in colon tissue, intestinal microflora diversity (Chao index, Shannon index and Simpson index), VIP, cAMP, PKA and the mRNA and protein levels of VIP, cAMP, PKA, aquaporin 3 (AQP3), mTOR, ribosomal protein S6 kinase (S6K1) in colon tissue were detected. Compared with UC group, the weight of mice increased, DAI score decreased, histopathological injury improved, colon length increased, MPO activity decreased, and Chao index, Shannon index and Simpson index increased in MIMBb75 low-dose group, high-dose group and Mesalazine group, the mRNA levels of VIP, cAMP, PKA, AQP3, the expression of VIP, cAMP and AQP3 protein and the phosphorylation level of PKA increased, while the phosphorylation levels of mTOR and S6K1 mRNA and protein decreased (P<0.05). Results: Compared with mimb75 high dose group, the mRNA levels of VIP, cAMP, PKA and AQP3 and the expression of VIP, cAMP and AQP3 protein and the phosphorylation level of PKA in MIMBb75 high dose combine VIP antigonist group decreased (P<0.05). The phosphorylation levels of mTOR and S6K1 mRNA and protein increased in MIMBb75 high dose combine MHY1485 group (P<0.05). VIP antigonist and MHY1485 could reverse the protective effect of MIMBb7 on UC mice, aggravate the colonic injury and increase the MPO activity (P<0.05). Conclusion: Bifidobacterium can improve colon damage and increase the diversity of intestinal flora in UC mice, which may be related to activation of VIP/cAMP/PKA pathway and inhibition of mTOR pathway. [ABSTRACT FROM AUTHOR]