Abstract: SD rats and three strains of mice were infected with Plasmodium yoelii yoelii By265 strain by intravenous inoculation of sporozoites via tail vein. Liver tissues were taken 42 hours after infection and serial sections were made and stained by Colophonium-Giemsa method for microscopic examination. The ratio of the average value of major diameter/ minor diameter of exoerythrocytic(EE)schizonts of Plasmodium yoetii yoelii in rats and mice of ICR/JCL, C57BL, KM strains was 35.81 ±4.56μm/29.72±4.08μm, 28.08±4.66μm/23.66±4.44μm, 28.14±.16μm/23.63±3.77μm, 23.80±2.42μm/21±0μm, respectively. The results showed that the development of EE schizonts of Plasmodium yoelii yoelii was not synchronous. The EE schizonts in the rat liver were surrounded by Kupffer cells, monocytes and monocyte-derived macrophages. Since the parasitemia disappeared rapidly in rats, and EE schizonts were not well developed in KM strain, it may be considered that ICR/JCL and C57BL strains are more suitable as vertebrate host in Plasmodium yoelii yoelii-Anopheles stephensi system model (Figs. 1-9).