Experiments were carried out to investigate the thermal performance of a rectangular duct with permeable ribs mounted on one of the principal walls. A horizontal rectangular duct with an aspect ratio (width/height) of 4:1 was examined. Multiple permeable ribs were attached to the bottom base surface of the channel. Constant heat flux was the boundary condition for the ribbed wall. The perforated ribs were placed periodically and transversely to the stream wise direction. The parameters investigated in the present work are rib open-area ratio (0, 10 and 20 percent), rib pitch to height ratio (5, 10 and 20) and Reynolds number ranged from 15,000 to 75,000. It was found that the perforated ribs provide a substantially lower drag force in comparison with the solid type ribs and still provide enhanced heat transfer coefficient in comparison with the smooth wall duct. The results indicated that the perforated ribs with open-area ratio of 20% in a lower flow Reynolds number range provide better thermal performance under a constant power constraint. New correlations were obtained for the effects of rib pitch to height ratio, rib open-area ratio and Reynolds number on both the heat transfer and friction similarity factors.