In the current study,thermal boundary conditions are considered in a rotating smooth channel with a square cross-section to investigate the secondary flow and compare it to that of the same channel without heating.The measurement is conducted at three streamwise planes (X=445 mm,525 mm,605 mm).The flow parameters are the Reynolds number (Re=4750,which was based on the average longitudinal or primary velocity U and the hydraulic diameter D of the channel cross-section),the rotation number (Ro=ΩD/U,where Ω is the rotational velocity,ranging from 0 to 0.26),and the aspect ratio of the channel cross-section (AR=1,which is calculated by dividing the channel height by the channel width).The leading and trailing walls are heated under a constant heat flux qw=380 W/m2,and the top and bottom walls are isothermal at room temperature.This work is in a series with our previous work without thermal boundary conditions.Based on the experimental data,we obtained a four-vortex regime.There is a counter-rotating vortex pair near the leading side and the trailing side.Because the leading and trailing walls are heated,the buoyancy force increases the relative vertical position of the vortex pair near the trailing side from 5％ to 12.5％ of the hydraulic diameter.When moving upstream along the streamwise direction,the upper vortex near the trailing wall becomes weaker,whereas the lower vortex becomes stronger.As the rotational speed increases,the vortex pair near the trailing side is inhibited by the Coriolis force.Under heated thermal boundary conditions,the vortex pair near the trailing side reappears due to the effect of buoyancy force.These results indicate that the buoyancy force has a substantial effect on the secondary flow regime under thermal boundary conditions.