In this paper, we experimentally investigated the mainstream and secondary flow in a smooth rotating channel with wall heated by particle image velocimetry (PIV). The hybrid effect of Coriolis force and buoyancy force on the mainstream and secondary flow was taken into consideration in the current work. In the experiments, the Reynolds number, based on the channel hydraulic diameter (D = 80 mm) and the bulk mainstream velocity (V-m = 1.82 m/s), is 10,000, and the rotation numbers are 0, 0.13, 0.26, 0.39, respectively. Constant heat flux on the four channel walls are provided by Indium Tin Oxide (ITO) heater glass, the density ratio (d.r.) equaling approximately 0.1. The buoyancy number ranges from 0 to 0.153. The results showed that Coriolis force and buoyancy force have important influences on the flow field in rotating channels. Coriolis force pushes the mainstream to trailing side, making an asymmetry of the mainstream. On the cross-section, there is a symmetric two-vortex pair caused by the Coriolis. The two-vortex pair is pushed into the trailing side with the increase of rotation numbers. Then, there are two small vortex appearing near the leading side. Buoyancy force suppresses mainstream and causes the separation of the flow near the leading side. When the separated flow happened, the structure of secondary flow is disordered near the leading side. (C) 2017 Elsevier Ltd. All rights reserved.