Fluidized bed treatment to adsorb mercury was discussed. The adsorption model to discuss kinetics was proposed. Over-all coefficient of mass tansfer was measured and its correlated equation was obtained. The simulation of concentration variation by the model was cbincident with experimental data. The multi-stage classification model was proposed to apply the adsorption model to particles with wide range of size. Fluidized bed treatment for actual wastewater was discussed. Concentration variation in the treatment was able to be simulated by the model that over-all coefficient of mass transfer obtained from experiments of actual wastewater was used.