lt is very important in Hydraulic Engineering as well as, in Fluid Hechanics to reveal the response of velocity profiles and bed shear stress to abrupt change of bed roughness in open chamlel flows. ln the present study, accurate velocity measurements over abrupt1y changed k-type roughness elements were conducted in open channel flows by making use of two-component laser Doppler anemometer. An inmer boundary layer develops from the boundary point (x=0) between smooth and rough beds. The velocity and turbulence distrlbutions in the inner boundary layer rapidly respond to abruptly changed roughness. of particular significance is that the bed shear stress overshoots immed iately downstream of the abrupt roughness change.This finding is very important to construct bed protection works in rivers.