Spanwise heat transfer in wall turbulence was studied in a turbulent channel flow having a linear spanwise variation of time-mean temperature just the same as the spanwise variation of wall-temperature. The results of direct numerical simulation (DNS) for various Prandtl numbers ranging from 0.1-1.5 were compared with existing DNS data for ordinary two-dimensional heat transfer from uniformly heated walls. The Prandtl number effect on the spanwise eddy diffusivity of heat was found to be quite similar to that on the wall-normal component. Similarity was also observed between the destruction of the spanwise turbulent heat flux and that of the wall-normal component.