Objective:To study the transfection and expression level of human NK4 gene in A549 cells by constructing NK4 of recombinant lentiviral vector, and observe the effect of NK4 on cell proliferation and apoptosis. Methods: The NK4 gene was cloned into lentiviral expression vector by recombining DNA technology. The recombinant plasmid was cotransfected with lentiviral packaged systems in 293T cells by lipofectin reagent to produce lentiviral particles. A549 cells were infected with the lentivirus, and the infection efficiency was observed under fluorescence microscope. Expression of NK4 gene and protein was identified by RT-PCR and Western blot, respectively. Three groups of cells were established, including the A549/NK4 group, the negative control group (A549/LV), and the blank control group (A549). Expression of c-met mRNA in the three groups of cells was examined by RT-PCR analysis. Through MTT colorimetric, we assayed the growth of the three groups of cells from the first day to the seventh day, and drew a growth curve to compare the proliferations of cells. The rates of apoptosis of the cells were detected by flow cytometry. Results: LV-NK4 transfected A549 cells expressed NK4, and the cells expressed less c-met than the blank and negative group. In MTT test, the A549/NK4 group cells grew slower than the other group from the fourth day (P < 0.05). With flow cytometry, the apoptosis rate of the A549/NK4 group was higher than the blank and negative control group. Conclusion: The NK4 recombinant lentiviral vector had been successfully constructed and effectively transfected A549 cells. NK4 can inhibit the proliferation and promote the apoptosis of A549 cells, the mechanism may be related to down-regulated c-met.