Abstract: A 54-kDa protein overexpressed by chloroquine-resistant Plasmodium berghei ANKA strain was first reported by us. In this paper, the localization of this protein by immunoelec-tron microscopy is presented. The results showed that the protein was mainly scattered inside the cytoplasm of the early date trophozoites and schizonts of erythrocytic stage of P. berghei ANKA strain , and some of it was also found in cytoplasm of erythrocytes infected with parasites. The protein content was much higher in chloroquine-resistant P. berghei ANKA strain than in chloroquine-sensitive P. berghei ANKA strain, suggesting the importance of this protein in understanding mechanism of chloroquine resistance in malaria parasites .