A study on the fructose production by immobilized whole cell glucose isomerase (GI) was performed in two kinds of hollow fiber reactors; dual hollow fiber reactor and dual circuit hollow fiber reactor. Cell immobilization was accomplished by growing $\underline{Arthrobacter}$ sp. cells possessing GI activity in the reactor. Feeding GI production medium and air to the cells immobilized in the reactor increased the cell biomass and as a result the enzyme activity. After biomass reaching a desired density, the cells were heat treated in-situ and the reactor was used as an enzyme reactor for conversion of glucose to fructose. The final cell mass in dual hollow fiber reactor after 6 days culture was 105g DCW/1. In enzyme reaction of dual hollow fiber reactor which was operated at substrate pH 9.0, temperature of $65\circ{C}$, and substrate flow rate of 4.0ml/h, the enzyme deactivation constant was $1.10\times 10^{-2}l/h$ and the average volumetric fructose productivity for 4 days was 7.61g/l h. This productivity was higher than any other productivities obtained at other operating conditions. At a lower flow rate the substrate flow distribution in the hollow fibers was not good, which resulted in lower fructose productivity. The modeling of hollow fiber enzyme reactor was done. Computer simulation with these modeling equations with $D_3$ value of $0.78\times 10^{-6}cm^2$/s gave result which fitted well the experimental data at a flow rate higher than 2ml/hr. The cell loading in the dual circuit hollow fiber reactor using 35 hollow fibers for air and liquid substrate circuits was 62 gDCW/l after 6 days culture. This is much lower than that of dual hollow fiber reactor As a result the productivity in dual circuit hollow fiber reactor was lower than that of dual hollow fiber reactor. The reason for this poor cell loading was that in cell culture period many cells leaked into the effluent and most of the cells were located at the bottom of the reactor because the space between the fibers was too large to retain the cells.
