Pulsatile blood flow using incompressible newtonian fluid is investigated numerically in abdominal aortic aneurysm models with the aid of transient Navier-Stokes equations for axisymmetric geometry. The arterial wall is assumed to be rigid. The actual arterial pressure-velocity pulse at the abdominal aorta is used as the inlet boundary condition to the aneurysm. The corresponding velocity at every time-step is assumed to be fully developed parabolic profile at the inlet. Time-dependent formation of vortices and occurrence of stagnation zones are analyzed in this numerical study. It has been found that the distal end of the aneurysm is subjected to maximum shear stress and pressure during the entire cycle. This analysis also confirms that the mechanical forces on the arterial wall, developed by the blood flow which is pulsatile in nature, may play an important role in both development and growth of aneurysms. It has also been found that a quasi-steady state may be used to explain sufficiently the basic flow characteristic within the aneurysm. The wall shear stress in the quasi-steady state at the distal end of the aneurysm during the most adverse condition was approximately the same as in the pulsatile state for a similar situation.