In order to investigate the optimum geometric conditions for a heat transfer augmentation technique using visco-elastic fluid, flow visualization experiments have been performed in a cavity between rectangular ribs. The rib height, the rib length and the cavity size were changed in several steps while the mean velocity at narrow cross-sections was kept constant. From the results, it is expected that the case having small rib height, small rib length and large cavity size has an advantage for heat transfer augmentation. It is also found that the recirculation size is a simple function of contraction ratio and Weissenberg number.