Abstract: AIM: To examine the effect of inoculated sporozoites of Plasmodium yoelii on the early cellular responses of rat liver. METHOD: Ultrastructure of rat liver was observed by transmission electron microscopy 30 minutes after inoculating with nine million sporozoites. RESULTS: Phagocytic activity of Kupffer cells(Kc) was increased. There were a lot of phagolysosomes in the cytoplasm of Kc. Blood platelets were swollen and adhered to Kc or endothelial cells and to form microthrombi. Some hepatic cells were damaged. The mitochondria of hepatic cells were vacuolated and the mitochondrial cristae were dissolved.There were cytolytic focal necrosis in the cytoplasm. CONCLUSION: Acute cellular responses of rat liver occurred 30 minutes after the inoculation of nine million of P. yoelii sporozoites. Some sporozoites were damaged by Kupffer cells. The ultratructural changes of mitochondria of hepatic cells contributed at least partly to the degeneration of exo erythrocytic stage of the parasite.