Blood cells are subject to various kinds of stresses in flow fields. Hemolysis is the phenomenon in which a higher stress than normal damages the erythrocyte membrane and results in the leakage of its contents. Even if the stress is not strong enough to cause cell lysis, however, the cell membrane may sustain some damage. Therefore, to further improve the blood compatibility of artificial organs, the mechanisms of sublethal damage must be investigated. As a first step, we have analyzed the fine surface structure of sheared erythrocytes from a microscopic viewpoint by using an atomic force microscope (AFM) featuring nano meter-scale visualization. Sheep erythrocytes were sheared by a conventional cylindrical viscometer under sublethal shearing conditions. The duration of shear was set at 10 s, and the shearing rate was set at 0 (as control), 10000, and 50000/s. After being stressed, the cell surfaces were visualized by an AFM and the surface roughness was measured. As a result, the roughness value was found to increase with the shearing rate: 4.5 +/- 1.5 nm (0/s, control), 6.9 +/- 2.1 nm (10000/s, P < 0.01), and 10.1 +/- 2.4 nm (50000/s, P < 0.01).