A gene encoding the thermostable acetylxylan esterase (AXE) in Thermobifida fusca NTU22 was amplified by PCR, sequenced and cloned into the Pichia pastoris X-33 host strain using the vector pGAPZ alpha A, allowing constitutive expression and secretion of the protein. Recombinant expression resulted in high levels of extracellular AXE production, as high as 526 U/mL in the Hinton flask culture broth. The purified enzyme showed a single band at about 28 kDa by SDS-polyacrylamide gel electrophoresis after being treated with endo-beta-N-acetylglycosaminidase H; this agrees with the predicted size based on the nucleotide sequence. About 70% of the original activity remained after heat treatment at 60 degrees C for three hours. The optimal pH and temperature of the purified enzyme were 8.0 and 60 degrees C, respectively. The properties of the purified AXE from the P. pastoris transformant are similar to those of the AXE from an E. coli transformant.