An intracellular glucose oxidase was isolated from the mycelium extract of a locally isolated strain of Aspergillus niger UAF-1. The enzyme was purified to a yield of 28.43% and specific activity of 135 U mg(-1) through ammonium sulfate precipitation, anion exchange and gel filtration chromatography. The enzyme showed high affinity for D-glucose with a Km value of 2.56 mM. The enzyme exhibited optimum catalytic activity at pH 5.5. Temperature optimum for glucose oxidase, catalyzed D-glucose oxidation was 40 degrees C. The enzyme showed a high thermostability having a half-life 30 min, enthalpy of denaturation 99.66 kJ mol(-1) and free energy of denaturation 103.63 kJ mol(-1). These characteristics suggest the use of glucose oxidase from Aspergillus niger UAF-1 as an analytical reagent and in the design of biosensors for clinical, biochemical and diagnostic assays.