Abstract: Objective To define the optimal dose of dexamethasone induced cleft palate in C57BL/6J mice and to provide a reliable model of cleft palate for further study. Methods Pregenant mice at specific period were divided into five groups randomly, that were control group and experimental groups of Ⅰ, Ⅱ, Ⅲ, Ⅳ. The mice of the control group were injected sodium chloride 0.1 mL and the mice of experimental Ⅰ, Ⅱ, Ⅲ, Ⅳ groups were injected dexamethasone of 12.0, 6.0, 3.2, 1.6 mg/kg respectively at 8:00 am on embryo 10 to embryo 12. To weigh
pregnant mice and embryos and record the number of embryonic resorption and cleft palate after pregnant mice were killed on embryo 17.5. Results Weight of pregnant mice was significantly different（P<0.05）, but the number of embryonic resorption and cleft palate had no significant difference between control group and experimental Ⅲ, Ⅳ groups（P > 0.05）. Incidence of embryonic cleft palate had significant difference between control group and
experimentalⅠ,Ⅱgroups（P<0.05）. However, incidence of embryonic resorption increased significantly in experimental Ⅰgroup（P<0.05）. There was no difference in embryonic weight among each group（P>0.05）. Conclusion 6.0 mg/kg is the optimal dose of dexamethasone to induce cleft palate in C57BL/6J mice.

Key words: cleft palate, dexamethasone, mice