Abstract: A full-length of cDNA copy of the T7 RNA polymerase was cloned into the EcoR I and Sal I sites of PCI-neo vector under the control of the human Cytomegalovirus (CMV) immediate-early enhancer/promoter and designated PCI-T7. BHK-21 cell lines expressing PCI-T7 were developed using conditional medium containing Geneticin (G418) for 2 weeks. A helper DNA plasmid, named as pT7 HN was co-transfected into VT7 cell and detected by Western blot. These results showed that the T7 RNA polymerase of the vaccine virus strain VTF7-3 was expressed in stable recombinant cell lines and VT7 cell line expressing T7 RNA polymerase stably at least 30 passages. The developed system would be offer an attractive and safe alternative to other inducible eukaryotic expression systems which provides an important platform for study of the rescue and function of NDV strain NA-1.