Roughness of vanes’ outer surface and that of cooling channels’ inner surface have considerable impact on temperature distribution. Using a rougher surface leads to increased turbulence in near-surface flows and increases the rate of heat transfer. In this study, vane of a C3X turbine cooled via 10 cooling channels was simulated -three-dimensionally- by ANSYS-CFX software based on SST turbulence model, and then the effects of roughness of said surfaces were examined. The results showed that increasing the roughness of the blade’s outer surface, which absorbs the heat of the hot fluid, to values below the threshold of fully rough regime ( Reks < 70 ) makes no significant impact on vane’s surface temperature distribution; but increasing the roughness to values higher than this threshold leads to 8% increase in surface temperature. This indicates that outer surface of the blade should always exhibit a transitionally rough regime. Opposite to the outer surface, increasing the roughness of cooling channels’ inner surface, which transfers the heat to the cooling fluid, found to be the very beneficial, as even a slight increase in the roughness of this surface (within the domain of transitionally rough) decreases the blade’s surface temperature by up to 8%, and improves the hydraulic-thermal performance factor by about 250%.