A genomic library of a mesophilic cellulolytic anaerobe, Clostridium sp. KCTC 8440 DNA was constructed in Escherichia coli using plasmid pUC9. Clones of E. coli exhibiting carboxymethyl cellulose-hydrolyzing activity (CMCase) were isolated and divided into seven types based on the restriction enzyme patterns of recombinant plasmids. E. coli strains carrying type A genes showed activity on carboxymethyl cellulose about 7-8 times greater than clones carrying genes of other types. Restriction maps of the cloned DNA fragments were determined, and homologies between them were investigated. The results suggest that Clostridium sp. KCTC 8440 has seven distinct CMCase genes.