The aim of this study was to evaluate in vitro and in vivo the effects of 2 brands of probiotic fermented milk on biofilms, oral microbiota, and enamel. For the in situ experiment, ten volunteers wore palatine devices containing four blocks of bovine dental enamel over 3 phases, during which 20% sucrose solution, Yakult ® (Treatment A), and Batavito ® (Treatment B) were dropped on the enamel blocks. Salivary microbial counts were obtained and biofilm samples were analyzed after each phase. For the in vivo experiment, the same ten volunteers drunk Yakult ® (Treatment C) and Batavito ® (Treatment D) in two phases. Saliva samples were collected for microbial analysis after each phase. The in situ study showed that in comparison with Treatment A, Treatment B resulted in fewer total cultivable anaerobes and facultative microorganisms in biofilms, higher final microhardness, lower percentage change in surface hardness, and smaller integrated subsurface enamel hardness. In the in vivo study, Treatment D resulted in a reduction in the counts of all microorganisms. The results suggested that the probiotic fermented milk Batavito ® , but not Yakult ® , reduced the amount of oral microorganisms and mineral loss in bovine enamel.