The blood flow in the vascular with a rough wall has been investigated numerically to examine the influence of the roughness on the vascular lesion from the hydrodynamical point of view. As a two-dimensional model of the blood flow in the vascular with a rough surface, the pulsatile flow in the rigid channel with several roughness elements which consist of a series of square ribs is considered, and the blood is assumed to be a Newtonian fluid. The Navier-Stokes equations (stream function-vorticity formulation) are solved by the finite difference method. The calculation is performed for the range of Reynolds number 300≦Re≦2000, but both the period and the amplitude of oscillation are fixed. In this paper, particular attension is paid to the flow pattern over the roughness elements, so the instantaneous stream lines of pulsatile flow are presented for the neighborhood of roughness elements. The influence of roughness on the vascular lesion is discussed from the structure of pulsatile flow over a rough wall.