This research studies the heat transfer in porous medium experimentally. Experimental investigation is carried out of free convection heat transfer for three dimensional in a box. The box filled with saturated porous medium, manufactured from glass with dimensions (30 × 30 × 30) cm. The porous media of plastic balls is used with homogeneous in diameter (11.7 mm). The lower wall of the box is heated by an electrical heater, while the other walls are thermally isolated. The effect of a porous medium on free convection heat transfer is studied for five values of heat fluxes (348, 576, 839, 1147, and 1384W/m2).Rayleigh number is ranging between () and for average Nusselt number between (). The results showed that the temperature inside the space increases as Rayleigh number increases. Also, the average Nusselt number increases with increase of Rayleigh number for the first three values of heat flux, but it decreases after heat flux because of domination of the conduction heat transfer on convection heat transfer. Also an empirical correlations were obtained in this study.