The blood flow in a large artery is commonly analyzed by means of constitutive equations. However, it is not appropriate to use these equations for small arteries because of the heterogeneity of the blood. In this study, we use a bead-spring model for an erythrocyte to simulate a low-hematocrit blood flow in a small artery with a stenosis. The flow field is solved using Euler coordinates, whereas the motion of the erythrocyte is solved using Lagrangian coordinates (two-way coupling). The results show that the erythrocytes are considerably deformed around the stenosis and that the separated region downstream of the stenosis is weakened by the erythrocytes.