A 16 kilobase (kb) HindIII fragment of alkalophilic Bacillus sp. YC-335 containing a gene for xylanase synthesis was inserted at the HindIII site of pBR322 and cloned in Escherichia coli HB101. After subcloning of recombinant plasmid pYS52, the 1.5 kb fragment was found to code for xylanase activity, and the hybrid plasmid was named pYS55. The DNA insert of the plasmid was subjected to restriction enzyme mapping, which showed that pYS55 had single site for PuvII and SstI in the 1.5 kb insert fragment. Southern hybridization analysis revealed that the cloned gene was hybridized with chromosomal DNA from alkalophilic Bacillus sp. YC-335. About 64% of the enzyme activity was observed in the extracellular and periplasmic space of E. coli HB10l carrying pYS55.