We are currently developing Lactobacillus reuteri isolated from healthy dogs as a probiotic supplement for canine atopic dermatitis (AD). In this study, we examined the anti-allergic effects of live L. reuteri and killed L. reuteri strain mixture (i.e., strains M01, M11, M40, and M41) using a hapten-induced-AD mouse model. First, when UV-killed L. reuteri (overgrowth) was orally administered to AD mice, cutaneous barrier function evaluated by the trans epidermal water loss was maintained as normal in the L. reuteri treatment group, compared with the control group. Immune reactions including lymphocyte proliferation in auricular lymph nodes and total IgE levels in serum are significantly regulated by treatment of killed L. reuteri. In contrast, L. reuteri treatment improve neither AD score nor skin thickness. Second, the anti-AD effects were examined using 4 individual strains of live L. reuteri (i.e., M01, M11, M40, or M41). The symptoms of AD and immune responses such as lymphocyte proliferation and total IgE levels are significantly reduced by L. reuteri M11 administration compared with the vehicle control and other strains. Currently, the interaction with macrophages and regulatory T cells is being studied.