Heat transfer results were presented for combined forced and natural convection around a heated cylinder placed in a cross-flow of water. Local heat transfer coefficients were measured in the range of Reynolds and modified Rayleigh numbers as 40<Re_d<1600, 3.0×10⁶<Ra_d<2×10⁸. The result demonstrates that the heat transfer rates increase on the rear side, and decrease on the front side of the cylinder with an increase in wall heat flux. The average Nusselt numbers for the combined convection become 20% higher than those estimated from the pure forced or natural convection. The enhancement and the retardation of the heat transfer rates are explained in terms of the local variation of the lower separation point due to buoyancy force. Furthermore, the average Nusselt numbers of the combined convection correlate well with the parameter Gγ_d/Nu_dRe_d², and the combined convection region corresponds to the value of this parameter of 0.1<Gγ_d/Nu_dRe_d²<20.