Ammoxidation of propylene to acrylnitril (Sohio process) was selected as a model reaction in order to study the effect of the hydrodynamic conditions in an industrial-scale fluidized-bed reactor on the selectivity and yield to an intermediate product. The fluidized-bed reactor was simulated applying a two-phase model. For describing chemical reactions a global kinetics determined for the Bi-Mo-O catalyst was chosen from the literature. The simulation results indicate that the mass transport limitation between bubbles and the emulsion phase as well as back-mixing of gas in the emulsion phase results in the drop of selectivity and yield to acrylnitril compared to the plug-flow and CSTR reactor. The possibility of the improvement of the reactor performance by varying particle diameter or by applying a multistage fluidized bed was also studied in the paper.