An extracellular β-xylosidase from the thermophilic fungus Paecilomyces thermophila J18 was purified 31.9-fold to homogeneity with a recovery yield of 2.27% from the cell-free culture supematant by ammonium sulfate precipitation,DEAE-52 and Q-Sepharose Fast Flow chromatographies.It appeared as a single protein band on SDS-PAGE with a molecular mass of approx 53.5 kDa.The molecular mass of β-xylosidase was 51.8 kDa determined by Superdex 75 gel filtration.The enzyme was a glycoprotein with a carbohydrate content of 61.5%.