Human leukocyte antigen-G(HLA-G) is a nonclassical major histocompatibility complex Ⅰ (MHC Ⅰ) molecule. As the ligand of NK inhibitor receptors, it can transmit the inhibitory signal and inhibit the cytotoxicity of NK cells. In order to study the effect of HLA-G1 on the recognition of effector-target cells, laser scanning confocal microscopy (LSCM) and flow cytometry were used to analyse the expression and function of full-length HLA-G1 and the real-time change of ［Ca²⁺］_i (free intracellular Ca²⁺ concentration) in the target cells. Results showed that full-length HLA-G1 was expressed in the cytoplasm and on the cytomembrane of K562, JAR and CHO cells. HLA-G1 partially inhibited the cytotoxicity of NK92 in a 4h-⁵¹Cr-release assay. The ［Ca²⁺］_i in the CHO and GFP-CHO (which expresses the green fluorescence protein) obviously rised after the addition of activated NK92. The expression of HLA-G1 inhibited this kind of rising. These results demonstrated that the rising of ［Ca²⁺］_i in target cells is necessary for the effective cell cytotoxicity. The immune inhibition function of HLA-G1 is possible closely related to the inhibition of ［Ca²⁺］_i in the target cells.