Experiments were conducted to investigate the effect of fluid injection on laminar flow and heat transfer characteristics in a one-porous-wall square duct. Uniform air flow at Re-0 = 400-2000 entered the duct with a cross section of 20 x 20 mm(2) and a ratio of the active injection length to the hydraulic diameter of 40. Pressurized air was injected through a thick layer of porous material for Row uniformity and a heated porous duct wall at injection rates Re-w = 5-20. All of the measured and deduced data, including the axial velocity profiles, the pressure drops, the friction factors, the porous wall temperatures, the outlet fluid temperatures and the Nusselt numbers, were presented and compared with the previous theoretical results. The deduced friction factors and Nusselt numbers from the experimental data were correlated within differences of +/-10% and +/-15% respectively.