Three-dimensional isothermal twin-screw extrusion with wall slip is simulated using the fluid dynamic analysis package POLYFLOW. Profiles of velocity contours in the screw channel and shear rate distributions in the intermeshing region are presented. Curves of axial pressure difference, average shear rate and dispersive mixing index vs. the slip coefficient are plotted and discussed. Comparisons are also made between the wall-slip conditions and the non-slip condition.