Abstract: A cDNA clone of PAP-sp1 with changed nucleotides within the N-terminal signal petide sequence was obtained by RT-PCR method from leaves of Phytolacca americana. The plant binary vector was constructed by inserting PAP-sp1 cDNA into the vector pBI121, which was then introduced into leaf explants of the tobacco variety K326 by Agrobacterium tumefaciens mediated method. Histochemical assay and PCR were employed to confirm the transgenic plantlets regenerated on screening medium, and the transformation efficiency was 8.1% counted by the number of regenerating explants. TMV mechanical infection test of the transgenic plants revealed that, in comparison to the control plants, the transgenic plants exhibited viral resistance by retarded symptoms of systemic infection, less mottled leaves and earlier blooming.