Abstract: The experiments on open-channel flows on the rough mobile bed in the transitional region are reported in this paper. The velocity in the flume were measured by a 22D LDA,and the resistance coefficient were calculated with the Einstein's resistance division method. The experimental results show that(1)The Karman constant in the Log-law of the open channel flows in the transition region is smaller than which that of the smooth open channel flows,and the integral parameter B does not coincide well with the Nikuradse's result from the pipe flows;(2)The weak bed load in the flume may cause the drag-reducing effect;and(3)The Reynolds stress and the turbulence distribution are similar to those in the smooth open channel flows.