One purpose of this study is to investigate the morphological change of endothelial cells in a separated flow area. The other is to reveal the albumin uptake into endothelial cells, the albumin uptake area, and the its content per unit area in the separated flow area. After 24 hr of exposure to flow induced in a back step flow channel, the endothelial cells were incubated in 37°C for 60 minutes in PBS containing tetramethylrhodamine isothiocyanate conjugated albumin (TRITC-albumin). Thereafter, the cell morphology, the density, and the albumin uptake were observed by a confocal laser scanning microscope (CLSM). In low shear stress areas (stagnant and reattachment areas), the cells are round and aligned randomly. In high shear stress areas (reversal and fully developed areas), the cells are elongated and aligned to flow direction. In low-shear-stress and high-shear-stress gradient areas (reattachment areas), the cell density is low compared to the other areas, and the amount of albumin uptake into the cells is the largest in all areas because of the increase of albumin uptake areas. These data indicate that shear stress and shear stress gradients affect the endothelial cell morphology and the albumin uptake into endothelial cells.