The purpose of this study is to reveal the albumin uptake into endothelial cells 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 and the albumin uptake were observed by a confocal laser scanning microscope (CLSM). In a low shear stress area (stagnant and reattachment areas), the cells aligned randomly. In a high shear stress area (reversal and fully developed areas), the cells were elongated and aligned to flow direction. In low-shear-stress and high-shear-stress gradient areas (reattachment areas), the amount of albumin uptake into the cells was the largest in all areas. These data indicate that shear stress and shear stress gradient affect the endothelial cell morphology and the albumin uptake into endothelial cells.