This paper aims to investigate the blood flow in a bell-shaped constricted rigid tube, modeled as stenosed artery. The flow is assumed to be axi-symmetric, laminar and of oscillatory type. A mathematical model of shear-thinning fluid corresponding to the shear-dependent blood viscosity (mainly due to the behavior of the red blood cells in suspension of the flowing blood) is considered. The governing equations of motion are presented with the help of stream function-vorticity and are solved numerically by finite-difference technique. The shear-thinning fluid model for the flowing blood has significant contribution in the dynamics of oscillatory blood flow. The results reveal that the arterial wall shear stress reduced significantly and the peak value of the wall shear stress at the maximum area reduction is comparatively low for Newtonian fluid viscosity. The lengths of recirculating regions formed after the constriction are reduced for the shear-thinning blood viscosity model and also for its different material parameters.