An experiment was carried out on free convective and radiative heat transfer from dense pin-fin arrays with a vertical isothermal base plate. Data analyses are made in consideration of the temperature distribution in the pin-fins, and of the radiative heat transfer. The free convective heat transfer characteristics of the pin-fin arrays are correlated fairly well with the Nusselt number and Rayleigh number, based on the horizontal spacing of the vertical pin arrays as a characteristic length. The generalized characteristics are similar to those of rectangular fin arrays. An experimental formula for the average heat transfer coefficient is derived.