Flow behavior of erythrocytes, especially the formation of marginal cell-free layer and the symmetrical (parachute-like) deformation of erythrocytes, was compared in microvessels and glass capillaries. Human erythrocytes were perfused through a part of microvascular network isolated from rabbit mesentery and hand-made glass capillaries. The thickness of marginal cell-free layer and the inner diameter of micro-flow channel were measured with an image analyzer. The symmetrical deformation of erythrocytes was recorded on videotape under flash light and analyzed with an image processor. Flow velocity of erythrocytes was determined on the basis of the traveling distance of an erythrocyte on the video-frame or by a dual-spot cross-correlation technique. The thickness of cell-free layer increased with an increase of the inner diameter of micro-flow channel. The cell-free layer at Ht ≥ 30 % was thinner in microvessels than in glass capillaries. With lowering the hematocrit or increasing the flow velocity of erythrocytes, the thickness of cell-free layer increased, and the increment was greater in microvessels than in glass capillaries. On the other hand, the length of symmetrically deformed erythrocytes in flow axis increased with increasing the flow velocity of erythrocytes, and the degree of the extension was greater in glass capillaries than in microvessels. The same tendency was observed for erythrocytes with decreased deformability. In conclusion, the flow dynamics of erythrocytes in microvessels is essentially different from those in glass capillaries.