The interaction of thermal radiation with laminar mixed convection for a gray fluid in a radially rotating square duct is numerically studied. The integro-differential radiative transfer equation is solved by the discrete ordinates method. The coupled momentum and energy equations are solved by the DuFort-Frankel numerical scheme. Results are presented in a radially rotating square duct over a wide range of the governing parameters. The effects of rotation-induced buoyancy and thermal radiation on the developments of velocity, temperature, friction factor and Nusselt number are examined in detail. The axial variations of the fRe and Nu are characterized by a decay near the entrance due to the entrance effect, but the decay is attenuated by the onset of the secondary flow. The predictions also demonstrate that the radiation presents significant effects on the axial distributions of the total Nusselt number Nu, and tends to reduce the centrifugal buoyancy effects. In addition, the heat transfer rate increases with the decrease in the conduction-to-radiation parameter N-c.