Centrifugal buoyancy effect on heat transfer in a rotating two-pass square channel with 180-deg sharp turns was numerically investigated by using the large eddy simulation. The effect of the aiding/opposing buoyancy contributions was seen in different longitudinal vortex structure near the pressure surface depending on the radial flow direction and in larger buoyancy-induced variation of the heat transfer on the pressure surface than that on the suction surface. As the buoyancy increased, the friction factor dominated by the pressure loss of the sharp turn decreased a little, and the Colburn's j factor stayed almost constant. As a result, the heat transfer efficiency index slightly increased by the buoyancy. (C) 2004 Elsevier Ltd. All rights reserved.