An experimental investigation was carried out to study the effect of artificial roughness on turbulent heat transfer in the entrance region of circular tubes, The experiments were performed via a mass transfer technique which simulated an isothermal-wall boundary condition for the analogous heat transfer problem. Prior to the onset of heat (mass) transfer, the how was hydrodynamically fully-developed. Nevertheless the heat (mass) transfer data were collected for the developing as well as for the fully developed regions. The artificial roughness was a two-dimensional rib roughness with pitch (P) to roughness element height (e) ratio between 3.33 and 80, and roughness height to tube inner diameter (D) ratio equal to 0.013 and 0.077. It was observed that for the best condition (St/St(s) approximate to 2.5 and f/f(s) approximate to 5, i.e. highest heat transfer to lowest possible pressure loss), Pie is between 13.33 to 20 and e/D is between 0.077 to 0.013.