In order to study the regulation mechanism of Sry in sex determination, the siRNA technique was used to silence the Sry expression in mouse embryos. Two siRNA expression vectors were synthesized, pSilencer4.1/Sry217 and pSilencer 4.1/Sry565. The siRNA expression vectors were injected into gestated mouse through tail vein. The sex was identified by PCR, and the expression level of Sry gene was determined using RT-PCR technique in the male mouse embryos at 11.5 dpc(days post coitum). The time- and dose -dependent effects was studied. The results confirmed that one of the siRNA expression plasmids, pSilencer4.1/Sry565, could inhibit the Sry gene expression significantly. Eighty-five percent inhibition was obtained when injecting 20 μg siRNA vector at 9.5 dpc.