The gene encoding the single cellulose-binding domain II (CBD II) of Clostridium stercorarium xylanase A was fused to the egIV gene encoding endoglucanase IV (EGIV) from Ruminococcus albus. The fusion protein (EGIV + CBDII) expressed in Escherichia coli can be readily purified from the cell-free extract of E. coli in a single step using the affinity of CBD to cellulose. The purified enzyme was cleaved into two moieties, i.e. the catalytic-domain and CBD, at a specific site in the linker region by partial digestion with trypsin at 4 degrees C. This result indicates that this CBD belonging to family VI of CBD families can be used as an affinity tag for purification of the recombinant protein.