A cellulase from the extreme obligate halophilic fungus, Aspergillus flavus, isolated from a man-made solar saltern in Phetchaburi, Thailand, was purified by ammonium sulfate precipitation and using Sephadex G-100 gel filtration column chromatography. The cellulase was found to be approximately 55 kDa by SDS-PAGE. Using CMC as a substrate, the specific activity of the cellulase was 62.9 units (U) mg(-1) with V-max and K-m values of 37.87 mol min(-1) mg(-1) and 3.02 mg mL(-1), respectively. Characterization of the enzyme revealed it to be an extremozyme, having an optimum activity at pH 10, 60 degrees C, and 200 g L-1 of NaCl. The enzyme activity was not significantly altered by the addition of divalent metal cations at 2 mM and neither did ss-mercaptoethanol, while EDTA was found strongly inhibiting the cellulase. Compared with commercial cellulase, the purified cellulase from A. flavus was more active in the extremity of conditions, especially at pH 10, 60 degrees C, and 150 g L-1 NaCl, whereas the commercial cellulase had a very low activity.