A new gene (named AP gene) encoding an alkaline serine protease with dehairing function was cloned from Bacillus pumilus UN-31-C-42 and its nucleotide sequence was determined. The expression of AP gene was induced with IPTG in Escherichia coli after the mature protease region was cloned into pET15b and SDS-PAGE showed expressed product clearly, but no alkaline protease activity was detected. In order to express the AP gene in B. subtilis, a recombinant expression plasmid was constructed which contained a promoter Bp53 (also from B. pumilus), the AP gene and an E. coli-B. subtilis shuttle vector pSUGV4. This plasmid was introduced into B. subtilis WB600 and the transformant displayed the hydrolyzed zone on a milk plate. The expressed product can be, easily detected with SDS-PAGE and the fermentation fluid of the transformant showed low alkaline protease activity and dehairing activity. This is the first report of a gene cloned from B. pumilus, encoding an alkaline serine protease, which can alone accomplish the whole dehairing process.