Abstract: Objective To investigate the therapeutic effect of natural killer cells(NK cells)on mice of primary liver cancer Heps transplant tumor and discuss the mechanism.Methods Mouse models of the solid tumor of liver cancer(Heps)were established.Then the mice were randomly divided into four groups:Normal saline(NS)group,treatment group 1(1×10⁴ NK cells/mouse),treatment group 2(1×10⁵NK cells/mouse),treatment group 3(1×10⁶NK cells/mouse).Each group has 15 mice.At the same day,different concentrations of NK cells were injected into the mice through the tail vein.The NS control group was administrated with the same volume of NS.Measure the implanted tumors volume as well as the mean survival time was calculated.Two mice from each group were sacrificed at the 15th day respectively.Tumor tissue samples were collected for routine pathological section,hematoxylin-eosin(H-E)staining.The spleen NK cells activity was estimated by LDH release assay;the activated NK cells in spleen were studied by flow cytometer(FACS).Results At the 8th day after inoculating,the growth situation of the tumor of group 3 was slower than that of other groups(P＜0.05).At the 20th day,the volume of the tumors was markedly decreased in the treatment group 1(P＜0.05),and the treatment group 2 and treatment group 3 are even more decreased compared with the NS group(P＜0.01).Treatment group 1 mice′ average survival is obviously longer than NS group and treatment group 2,3(P＜0.01).Compare with the NS control group′s NK cell in splenic,the treatment groups are obviously higher(P＜0.01).The lethality of the splenic was obviously enhanced in the treatment groups than that in the NS control group.Conclusions Moderate NK cells can effectively restrain the growth of Heps hepatocellular carcinoma transplantation,and extend the mice survival.It′s a experimental basis for the clinical application of NK cells.