Abstract: With scanning electron microscope, the surface structure of erythrocytes of the normal mice, of the mice infected with P. berghei and the erythrocyte-free parasites was observed. The results revealed three types of alterations on the surface of about 25% of the erythrocytes infected with P. berghei: 1. Obvious deepening of the ery-throcytic concavities; 2. small and deep invagination of the erythrocyte surface membrane; 3. crater-like pits on the erythrocyte surface. All of the altered portions mentioned above are named as "metabolic window". The erythrocyte-free P. berghei has a relatively smooth surface. The free malarial parasites are spherical with an average diameter of 3.2μm.Qinghaosu at the oral dose of 1.2g/kg had no appreciable effect on the surface of normal erythrocytes nor on that of the erythrocytes infected with P. berghei. Furthermore, no marked changes on the free malarial parasites were found 4 hours after the medication of qinghaosu. However, the erythrocyte-free parasites became significantly smaller and irregular in shape in the late period under qinghaosu action.