Lactobacillus is one of the bacteria strains which has been widely used in human life, has valuable probiotic properties. In the present study, L. reuteri FLRE5K1 was isolated from healthy mouse kidney and tested for its anti-melanoma activity in cell assays and animal models. The results showed that L. reuteri FLRE5K1 could significantly reduce the incidence of melanoma from 70 % to 30 % and significantly prolonged the survival of tumor-bearing mice. Despite of its significant effect on melanoma prevention, the tumor mass remained uneliminated. The alanine aminotransferase (ALT) level remained normal in tumor-bearing mice with intragastric administration of L. reuteri FLRE5K1, indicating that L. reuteri FLRE5K1 could prevent melanoma cells from damaging the liver. Cell assays showed that melanoma cells were inhibited by serum from mice with intragastric administration of L. reuteri FLRE5K1, but not by the bacteria itself. Further examination revealed that the levels of TNF-α and INF-γ in this serum were significantly increased. In summary, it was speculated that L. reuteri FLRE5K1 could stimulate the body to produce anti-cancer cytokines, inhibit the migration and colonization of melanoma cell line B16-F10, so as to prevent the onset of melanoma and prolong the survival of mice. The experiment was a useful complement to functional studies of endogenous probiotics and provided theoretical data support for the development of new microbioecologics.