Objective To explore the effects of knocking down ULF gene on the apoptosis of non-small-cell carcinoma H1299 cell after treatment with etoposide.Methods Three ULF small interfering RNA(siRNA)sequences and one negative control siRNA sequence were designed and synthesized, and then individually transfected into H1299 cell via lentivirus.The interference efficiency of ULF-siRNA were screened by real-time PCR and Western blotting.Then the most target siRNA was used for apoptosis assay after treatment with etoposide,MTT assay for H1299 cell proliferation,flow cytometry for cell cycle distribution. Results The expression of ULF gene and its protein ULF were down-regulated in H1299 cell when transfected with ULF-siRNA,and ULF-siRNA-1 was the most effective one,which had the highest inhibition rate(80%)of ULF expression.Compared with negative control group,ULF-siRNA group showed an obvious apoptosis after treatment with etoposide,and the inhibition rate of was higher than control group,which was positively correlated with etoposide dose,the difference was statistically significant(P<0.05 ).Flow cytometry showed that compared with the control group,G0/G1 cell cycle in ULF-siRNA group was increased,and S phase cells was decreased,the differences were all statistically significant(P<0.05).Conclusion Down-regulation ULF protein expression through treatment with etoposide can induce apoptosis of non-small-cell carcinoma H1299 cells,and inhibit cell proliferation,which lead to cell cycle arrest.ULF gene may become the new target of gene therapy for cancer.