The present work is concerned with a numerical study on laminar mixed convection flow and heat transfer in the entrance region of rotating isothermal rectangular ducts. The emphasis is placed on the rotational effects, including both the Coriolis force and centrifugal buoyancy, on non-isothermal flow and related heat transfer. The numerical results are presented for air flow in rectangular ducts over a wide range of the parameters. By examining the local field-solutions, the mechanisms for influences of Coriolis and centrifugal buoyancy forces can be addressed in detail. The results reveal that the variations of the local friction factor and heat transfer rate are closely related to the emergence, disappearance! growth, and decay of the rotation-induced secondary vortices. The friction factor and heat transfer rate can be enhanced by Coriolis effect. The predictions also demonstrate that the centrifugal buoyancy presents remarkable effects on the axial evolution of secondary Vortices and, therefore, on the flow and heat transfer characteristics in a radially rotating duct. The buoyancy effects are different on the trailing, leading and side walls; and the rotational effects can be altered with the change in cross-sectional aspect-ratio.