Objective To observe the changes of proportion of NK cells,?? T cells,CD4+CD25+T cells and their FOXP3-expressed sub-population in peripheral blood of acute Plasmodium vivax infected patients.Methods The proportions of NK cells,?? T cells,CD4+CD25+T cells and FOXP3-expressed sub-population within CD4+CD25+T cells were measured by flow cytometry(FCM)in peripheral blood of 25 patients with acute infection of Plasmodium vivax(AC)and compared with those of both 14 normal controls(NC)and 13 immune controls(IC).Results The proportion of NK cells in AC(8.48%)decreased significantly compared with that in NC(15.53%)and IC(17.69%)(P0.05).Conclusions During acute Plasmodium vivax infection,the proportion of NK cells decreases and the proportion of ?? T cells increases,and CD4+CD25+FOXP3+T cells decrease a little.