Objective To overcome difficulties in passage for SV40T transgenic mice, two genes containing different fragments of SV40T were constru cted: one gene is called SV40T-DRb which was mutated in Rb motif of SV40 T, another gene is called SV40T-Dp53 which was deprived of p53-binding d omain. Methods U sing recombi nant DNA techniques, the two changed gene fragments of SV40T were sequenced and cloned, and finally the two genes were cloned into the mammary gland-specific e x pression vector-p205C3. Microinjection of the expression vectors into male nucl e i was used to establish transgenic mice. PCR and Southern-blot were used to det e ct the positive transgenic mice, avoiding the occurrence of false positive trang enic mice. Results Six transgenic mice that were positive for b oth gene SV40T-DRb and gene SV40T-Dp53 were detected by PCR. One transgenic mouse that was positive for both gene SV40T-DRb and gene SV40T-Dp53 was detected by Southern blot. Co nclusion The above mentioned findings suggested that the two gene const ructs con taining different fragments are successful and the transgenic mice are surely wi th reduced tumorigenesis of SV40T.