Abstract: Objective 　To study invitro cytotoxic activity of NK-92 cells against human cervical cancer cells and effect of irradiation on NK-92 cytotoxicity. Methods 　NK-92 cells were mixed with ⁵¹Cr-labeled Hela or K562 cells at different effector-to-target ratios for a 4h ⁵¹Cr-release assay. On the other hand, NK-92 cells were irradiated at 0 and 400 cGy and tested after 2d for cytotoxicity against K562 and Hela cells. Results 　NK292 cells (0 cGy) displayed high invitro cytotoxicity against Hela with a mean specific lysis of 47 % and 50 % at 10∶1 and 20∶1 E∶Tratios, while these levels at 1∶1 (15 %) and 5∶1 (33 %) E∶T ratios were lower ; The cytotoxicity of N K292 against K562 ranged from 33 % to 69 %. N K 3/ 92 cells maintained up to 14 %～47 % cytotoxicity against Hela and 30 %～60 % cytotoxicity against K562 when irradiated with 400cGy after 2d. Conclusion 　In vit ro cytotoxic activity of NK-92 cells against Hela cells is high at suitable E∶T ratios, and substantial cytotoxicity can be retained up to irradiation dose of 400cGy.