The convective heat transfer in a rotating rectangular channel with an aspect ratio of 4:1 is investigated. Two branches of coolant enter the channel from the inlets at the top and bottom of the channel, encounter each other in the middle of the channel, and then exit the channel through eight sidewall slots. The channel is assembled in a rotating facility, and the two streams of flow are radial-outward and inward respectively. The mass flow rate of the major inlet is kept at a constant (Re = 20,000), whereas the inlet mass flow ratio (MR, second inlet mass flow rate/major inlet mass flow rate) changes from 0 to 0.6. The general MR is found to be a good parameter to describe the flow status in the two-inlet channel. However, with the local MR, the heat transfer data at different locations converge into the same trend, indicating that the local MR should be the dominate parameter. In the non-rotating channel, the Nusselt number ratio is oscillating against local MR, three extreme values can be distinguished at three critical local MR regardless of the location. In the rotating channel, a different kind of critical MR phenomenon is observed. After the critical point, the heat transfer on the leading surface exceeds the trailing one. A lower critical inlet MR is observed at a higher radius location, but the corresponding critical local MR is independent of location. The rotation suppresses the radial-inward flow and in turn results in a higher critical MR. (C) 2016 Elsevier Ltd. All rights reserved.