A β-lactamase gene was cloned from Streptomyces cellulosae as a 2.3-kb DNA fragment using Streptomyces lividans 1326 and PIJ385 as a host-vector system. During the course of cloning, a part of the chromosomal DNA fragment cloned together with a part of the vector plasmid were deleted, indicating instability of this contiguous DNA region. The enzyme from the clone showed similar properties with respect to binding of blue dextran and isoelectric point to the enzyme from S. cellulosate. The cloned gene hybridized not only to DNA of S. cellulosae, the source of DNA, but also to DNAs of several Streptomyces species, irrespective of their formation of β-lactamase. These results suggest that this gene may have homology to genes other than the one for β-lactamase.