Abstract: Objective 　To study the effect of natural killer (NK) cells on tumor growth inhibition of human nasopharyngeal carcinoma cell (CNE2 ) xenograft in BALB/c nude mice. Methods 　HLA typing of CNE2 cells and KIR (killer cell immunoglobulin-like receptor) genotypes were determined by PCR-SSP. Cytotoxicity of NK cells (isolated f rom 3 healthy persons ) against CNE2 cells were detected by LDH releasing assay. 12 BALB/c nude mice were divided into two groups ( the control group and the treatment group), 6 BALB/c nude mice in the treatment group were injected subcutaneously 1 ×10⁶ CNE2 cells together with 3 ×10 NK cells were injected intravenously into the tail veins, while the cont rol group were just injected 1 ×106 CNE2 cells subcutaneously. The changes of tumor volume were observed, and the tumor growth inhibition was calculated. Results 　The HLA genotypes of CNE2 cells were A2, 24, B18, 35, Cw4, 7. KIR genotypes of the 3 healthy persons were KIR2DL1, KIR2DL3, KIR3DL1, KIR3DL2.Cytolysis of NK cells against CNE2 cells in vit ro were (9. 37 ±2. 14) %, (27. 14 ±1. 82) %, (36. 40 ±4. 28) % and (54. 67 ±2. 80) % respectively at 5∶1, 10∶1, 20∶1, 30∶1 E: T ratios. NK cells significantly inhibited the tumor growth in vivo, in the cont rol and treatment group, the rate of tumor formation were100 %(6/ 6 ), 83. 33 % ( 5/ 6 ), respectively ; the time of tumor formation were ( 18. 80 ±1. 64 ) d, (10. 00 ±2. 68) d, ( P < 0. 01) ; the average weight of tumors were (2. 22 ±0. 09) g, (1. 42 ±0. 09) g, ( P< 0. 01), respectively, The growth inhibitory rate was 36. 04 %. HE stain show that there were more necrosis regions and keratinization of tumor cells in the treatment group than that in the control group. Conclusion 　Our findings suggest that NK cells can inhibit the human nasopharyngeal carcinoma xenografts in nude mice and may become a novel treatment approach for human nasopharyngeal carcinoma.