A numerical model based on the kinetic theory of granular media has been tested to simulate the unsteady two-phase flow in solid liquid fluidized beds. We focus here on the local unsteady flow features as predicted by the model and comparison with experimental data of Zen it and Hunt (2000) are discussed. In most of the cases, a series of two-dimensional rotational structures develops along the bed height, which controls the instantaneous solid fraction field as well as the level of fluctuating kinetic energy of the particles. Interestingly, with high inertia particles and at high solid concentration, these structures disappear to the benefit of a one-dimensional oscillating flow. The shape of these concentration waves is very similar to those previously observed by Nicolas et al. (1999) and Duru et al. (2002). The solid fraction density spectrum and variance have been analyzed and compared with the experimental data of Zenit and Hunt. (C) 2010 American Institute of Chemical Engineers AIChE J, 56: 2781-2794, 2010