Objective To investigate the characteristics of inhibitory and activating receptor expressions on natural killer ( NK) cells in HIV/HCV co-infected patients. Methods Numbers, frequencies and expressions of activating and inhibitory receptors of NK cells were measured with flow cytometry (FCS) from HIV/HCV co-infected group (n = 24), HCV mono-infected group (n=34), HIV mono-infected group ( n = 21 ) and healthy control group ( HC,n = 20) , then analysis and compare were performed among those groups. Results The NK cell absolute counts in HIV/HCV group were significantly lower than those in other three groups. The NKP30 and NKP46 frequencies on NK cells in HIV/HCV, HIV and HCV groups were all significantly lower than those in HC group, but there were no significant differences of NKP30 among former three groups; and NKP46 frequencies in HIV/HCV and HIV groups were lower than those in HCV group, but there were no significant differences between former two groups. The NKG2A frequencies in HIV/HCV and HCV groups were all higher than those in HIV and HC groups significantly, but the NKG2A frequencies in HIV group were lower than those in HC group; There were no significant differences of NKG2D,CD158a and CD158b among those four groups. Conclusion NK cell numbers and expressions of activiting receptors on NK cells obviously decreased in HIV/HCV co-infected patients, but some inhibitory receptors expressions increased, even higher than those of HIV mono-infected patients. NK cells impairments in HIV/HCV co-infection is more severe than HIV or HCV mono-infection.