A cDNA encoding FI-carboxymethylcellulase (FI-CMCase) of the fungus Aspergillus aculeatus was expressed in Saccharomyces cerevisiae under the control of the glyceraldehyde-3-phosphate dehydrogenase gene (GAP) promoter of S. cerevisiae. The transformed cells were able to secrete FI-CMCase efficiently into the culture medium as active enzyme. The recombinant FI-CMCases were observed to be two different enzymes of different molecular mass, one of which corresponded to native FI-CMCase (non-glycosylated FI-CMCase) and the other of which was an N-glycosylated protein (glycosylated FI-CMCase). The recombinant glycosylated FI-CMCase showed a higher thermostability than that of the native enzyme, although the former showed slightly lower activity toward the substrate than the latter.