A thermostable extracellular serine protease from Aspergillus fumigatus was purified 8.8-fold using a 4-step protocol. The enzyme was produced using a 36 h solid-state culture, had a molecular weight of 88 kDa and exhibited maximal enzyme activity at pH 7 and 60 degrees C. Structural analysis revealed that the protease is monomeric and non-glycosylated. Thermal inactivation of the pure enzyme followed first-order kinetics. The half-life (t(1/2)) of the pure enzyme at 50, 60 and 70 degrees C was 65, 34 and 14 min, respectively. The denaturation and activation energies were 69 and 62 kJ mol(-1), respectively. Thermodynamic parameters (entropy and enthalpy) suggested that the protease was highly thermostable. This is the first report on the thermodynamic parameters of proteases produced by A. fumigatus. (C) 2011 Elsevier Ltd. All rights reserved.