The purposes of this experiment were to investigate biomass characteristics and substrate re-moval efficiency and to find the optimum conditions on holding up higher biomass concentration in Fluidized-Bed Biofilm Reactor(FBBR). A number of experiments were conducted under the following conditions by increasing organic loading rate from 10kg COD/m³ㆍday to 80kg COD/m³ㆍday. Superficial upflow velocity was 17m/hr, operating temperature was 22±1℃ and pH was 7±0.1. The synthetic wastewater based on glucose was used as a substrate in this experiment. The removal of chemical oxygen demand(COD) with volumetric loading rates of 10kg COD/m³ㆍday was investigated to show the efficiency of aerobic FBBR. The corresponding COD removal efficiencies were 96 and 73% with volumetric loading rate of 10 to 80kg COD/m³ㆍday, respectively, and the concentrations of biomass remaining inside the reactor were shown 6,500mg/l and 37,000mg/l, respectively. These experimental conditions of the F/M ratio of 1.7 and the biofilm thickness of 420㎛ was proved to be a most appropriate condition in operating FBBR in the view of substrate removal.