A heterogeneous model describing the glucose isomerization process in an immobilized enzyme, fluidized-bed bioreactor was developed, The model without any adjustable parameters was used to predict the isomerization process. An excellent agreement between model predictions and experimental data for two isomerases (PG-GI Complex and Sweetase) obtained from the literature was found. The key parameters which measured the extent of external and internal mass-transport resistances, as well as the degree of back-mixing were quantified and discussed The effects of some operating and design parameters on the performance of the fluidized-bed bioreactor were also analyzed.