The present study is focused on investigation of heat transfer from a porous plate by cooling of air and surface with transpiration cooling. Effects of Reynolds number of hot air (Re= 3035, 3200, 3300, 3580), effects of flow rate of water as a coolant (ṁwater= 0.000083, 0.000116, 0.000166, 0.000249 kg/s) on local wall temperature and cooling efficiency of porous flat and the system inside a rectangular channel with air as a hot gas stream and water as a coolant were investigated numerically. In this study; different from the literature, transpiration cooling was used as a cooling mechanism of air. It was observed from the results that increasing Reynolds number causes an increase on surface temperature and a decrease on cooling efficiency of porous plate and system. Increase of Reynolds number from Re=3035 to 9430 causes a decrease of efficiency of the system of 13.7%. Increasing water flow rate nine times causes not only a decrease on average surface temperature of 1.1% but also an increase of 6.5% on efficiency of porous plate and an increase of 19.1% on cooling efficiency of the system. Numerical results prepared by RNG k ε turbulence model generally have a good approximation with experimental results.