Abstract A numerical study is performed to examine the transpiration-wall effect on mixed convection in a radially rotating multi-pass square duct connected with 180° sharp returns. Uniform injection or suction is applied to the leading wall of the rotating duct. Finite-difference method is adopted to solve three-dimensional Navier–Stokes equations and the energy equation. Periodic conditions are used between the entrance and exit of a typical two-pass duct for the closure of the elliptic problem. As predicted, results show that the radial distance from the rotational axis to initiation of flow reversal in the radial-outward duct (ROD) decreases with increasing rotational buoyancy. The appearance of flow reversal is delayed by the leading-wall blowing but is quickened by the leading-wall suction. The wall-blowing rate for avoiding the flow reversal in the ROD increases with increasing rotational buoyancy. Moreover, the axial distribution of peripherally averaged Nusselt number is closely related to the development of cross-flow intensity. They are increased/decreased with increasing the wall blowing/suction rate in the ROD but are essentially unaltered in the radial-inward duct (RID).