Carbon sources and nitrogen sources are known to be very important in protease production by microorganisms. The effects of carbon source and nitrogen source on protease biosynthesis by Bacillus licheniformis were investigated using batch cultures. As initial carbon and nitrogen concentrations of culture medium increased, the specific growth rate of Bacillus licheniformis was increased, while the specific protease production rate was decreased. From the results of batch cultures, a mathematical model which considers the effects of carbon source and cnitrogen source was proposed and the methods to increase the productivity of protease were discussed.