Abstract: This paper reports that tumor necrosis serum (TNS) containing tumor necrosis factor (TNF) could inhibite Plasmodium falciparum in vitro, TNS was obtained from rabbits given macrophage-activiting agent Mycobacterium tuberculosis (BCG)followed by intravenous administration of bacterial endotoxin (LPS). The results showed that TNS dilutions of 1:3, 1:6 and 1:12 cauld induce disappearance of Plasmodium falciparum (P0.05) after being cultured 6 hours. TNS decreased red blood cell infective rate of the parasites as compared with the control (P0.05) after 12 hours' cultivation. TNS of 1:3 dilution had further effect at 24 hours (P0.05). Morphological observations showed that the growth of schizonts was retarded and abnormal merozoites were found.