Abstract: The piperaquine-resistant strains of rodent malaria can be of value in the screening and development of new antimalarial compounds for the treatment of human falciparum malaria caused by resistant strains. This report describes the fine structure of the blood stages of the piperaquine-resistant line (PR line) of Plasmodium berghei ANKA strain. The ED50 on the PR line used was 197-fold greater than that on the parent line. The results showed that the PR line contained 3-4 food vacuoles in each trophozoite as compared with only one in most normal trophozoites. The membrane of the abnormal food vacuoles was swollen. Multilamellate whorl membranes were formed. The inter-membranous space between the outer and inner nuclear membranes was widened. Mitochondria endoplasmic reticulum has increased. Ribosomes, both free and membrane- bound, were closely clustered. The enlarged phagocytic vacuoles contained round or oval ball-like pigment granules in clusters,being markedly different from the typical rectangular, crystalloid pigment granules in parent line. No significant difference was observed in early trophozoites (ring form), schizonts and gametocytes between the PR line and the parent line.