In this paper, we have proposed a new non-linear constitutive model for blood with a viscosity which depends on the shear rate and the volume fraction of red blood cells or RBCs (hematocrit). The viscosity correlation is obtained from the experimental data reported in the literature. The governing equations for flow between two flat plates are made dimensionless and solved numerically. A parametric study is performed to study the effect of the four non-dimensional numbers K 1 (a relative measure of the pressure gradient to viscous forces), K 2 (a relative measure of gravitational force to pressure gradient in the direction of the gravity), N (dimensionless average hematocrit of blood), and ϕ m (maximum packing fraction of RBCs). The results show good qualitative agreement with other studies. © 2019 Elsevier Inc.