Liquid–solid binary fluidized beds are widely used in many industries. However, the flow behavior of suchbeds is not well understood due to the lack of accurate experimental and numerical data. In the currentstudy, the behavior of monodisperse and binary liquid–solid fluidized beds of the same density but dif-ferent sizes is investigated using radioactive particle tracking (RPT) technique and a dense discrete phasemodel (DDPM). Experiments and simulations are performed in monodisperse fluidized beds containingtwo different sizes of glass beads (0.6 and 1 mm) and a binary fluidized bed of the same particles for vari-ous bed compositions. The results show that both RPT and DDPM can predict the mixing and segregationpattern in liquid–solid binary fluidized beds. The mean velocity predictions of DDPM are in good agree-ment with the experimental findings for both monodisperse and binary fluidized beds. However, the axialroot mean square velocity predictions are only reasonable for bigger particles. Particle–particle interac-tions are found to be critical for predicting the flow behavior of solids in liquid–solid binary fluidizedbeds.