Objective To determine the influence of serum complement and IgG on rituximabdependent NK cell-mediated cytotoxicity to Raji cells in vitro.Methods FcγR Ⅲ a (CD16a) polymorphism of NK cells were detected by nest-PCR. Effects of serum IgG on FcγRⅢ a expression of NK cells in vitro were analyzed by flow cytometry.The target cells(Raji cells) were stained with DIO,cultured with effector cells(NK cells) and rituximab with or without serum IgG/complement,and finally stained with propidium iodide (PI),then these cells were tested by flow cytometry and the cytotoxic index was calculated as well. Results The cytotoxic indexes of the ADCC +CDC groups were higher than those of ADCC groups, but the serum IgG groups were lower than the ADCC groups. In FcγRⅢa-158Ⅴ/Ⅴ groups, the cytotoxic indexs of the ADCC+ CDC groups,the serum IgG groups and the ADCC groups were (94.25±1.79) ％,(59.79±0.66) ％ and(69.05± 2.38) ％,respectively,and the differences among the groups were statistically significant (P＜ 0.05).In FcγRⅢ a-158Ⅴ/F groups,the cytotoxic indexs of these three groups were (66.71±5.57) ％,(18.13±2.99) ％ and (39.63±3.86) ％, respectively, and the differences among the groups were also statistically significant (P＜ 0.05).Conclusions Complement may enhance the rituximab-mediated NK cell cytotoxicity to Raji cells, whereas,serum IgG may weaken the cytotoxicity against Raji cells. It is clued up that for patients treated by tumorspecific monolonal antibody (MAb), combined infusion of fresh frozen plasma could promote its anti-tumor effect,however,MAb combined with IVIG may impair its anti-tumor effect.