Objective： In order to evaluate the mechanism of allergen hypersensitivity. Methods： A mouse model of BALB/C sensitized by αs1-casein was established by oral gavage， and the levels of specific IgE antibodies were used to identify this animal model. The contents of mast cell proteinase， histamine and cytokines in mice were determined， and the clinical and pathological sections were observed. Results： The levels of specific IgE in each group mice increased significantly after the last large dose of αs1-casein was administered to mice at 42th day， and had different degrees of allergic symptoms. Moreover， the allergic reaction in medium and high dose group was stronger than that in low dose group. The levels of mast cell proteinase， histamine， IL-4， IL-5， IL-10 and IFN- gamma cytokines in sensitized mice were significantly higher than those in negative group， and increasing with the accumulation of sensitizing doses. The histopathological section showed that in the medium and high dose groups immunized with αs1-casein， the mice showed obvious inflammatory response， the local alveolar septum collapsed or thickened， and lymphatic foci were produced in the spleen and thymus， and the inflammatory cells infiltrated in small intestinal mucosa mesenchyme. Conclusions： Based on the BALB/C mouse model， the allergic mechanism of alpha αs1-casein was further revealed.