Objective:To study the influence of different culture conditions on charcic and inhibition activity of nature killer cells ( NK) ,whether to join the modified K562 cells with IL-6 cytokine.Methods:According to the 5′end of the human IL-6 cDNA sequence,PCR primers designed to amplificate,express and transfect K562 cells cDNA library as a template for DNA.Genetic modified K562 cells as stimulating cells were prepared by expressing IL-6.To extract peripheral blood mononuclear cells( PBMC) from human peripheral blood.PBMC were explanted by genetic modified K562 stimulated.The expansion was initiated by CO-culture of PBMC and irradiate genetic modified K562 cell.The number of NK cell increased by directed induced generation of genetic modified K562 cell.Immunophenotypic analysis of NK cell surface markers was performed by flow cytometry (FCM).51Cr release assay was employed to measure the specific lysis skilling of NK cell target K562 cells.Results:We have constracted genetic modified K562 cells by genetic engineering.As stimulated cell added into the PBMC,an average of 760 ±18 fold expansion of CD56+CD16+CD3-cells was observed after 3 weeks of co-culture system.The NK cells population could proliferated more 91%±2% after expansion comparing with 6%± 0.4%in PBMC before expansion by FCM.The cytotoxical activity of NK cells which was induced by genetic modified K562 cell was the strongest than induced by IL-6 cytokine alone.The expanded NK cells lysed 92%±2% of K562 targets in a 5∶1 effector to target ratio.In this case,the NK cells induced by genetic modified K562 cells against tumor cells was more lethal.Conclusion:PBMC based in vitro expansion of natural killer cells was set up by genetic modified K562 cells.The cytotoxicity of NK cells was the strongest induced by genetic modified K562 cell treated.These results had important guiding significance for the the NK large number of amplification and used in clinical.