To investigate the effect of the H-2Kd gene on the lymphocyte membrane, we constructed a small interfering RNA (siRNA) that targets the H-2Kd gene and compared the cytotoxicity of mouse lymphokine-activated killer (LAK) cells with different H-2Kd expression states. H-2Kd-targeting siRNA was transfected into spleen lymphocytes of BALB/C mice. Flow cytometry (FCM) was then performed to examine the expression of the H-2Kd gene in the transfected and control cells. Additionally, the cytotoxicity of the transfected cells toward the H22 and K562 cell lines was evaluated in vitro using the LDH release assay. H-2Kd-targeting siRNA significantly reduced the expression levels of the target protein, whereas pure transMessenger and non-silencing siRNA did not inhibit H-2Kd expression at the concentrations tested. The cytotoxicity of siRNA-treated LAK cells toward H22 and K562 cells was reduced significantly. The knockdown of H-2Kd gene expression by siRNA may be associated with LAK cell cytotoxicity toward neoplasm cell lines.