This study is concerned with flow chracteristics in a gradually expanding smooth rectangular open channel. The spatially evolution of mean velocity-, Reynolds stress-, and turbulent intensity-profiles in the longitudinal direction were investigated experimentally. Cole's wake parameter is expressed as a function of the pressure gradient, assuming the entire mean velocity profiles to be described by Cole's law. It is found that the distributions of Reynolds stress and turbulent intensities under the adverse pressure gradient differ substantially from these in the favorable pressure gradient.