The components of the media used to elicit the biosynthesis of $poly-{gamma}-glutamic$ acid $({gamma}-PGA)$ by Bacillus subtilis ZJU-7 were investigated, particularly the carbon and nitrogen sources Of the 7 carbon sources investigated, sucrose induced the highest rate of ${gamma}-PGA$ productivity; among the nitrogen sources, tryptone had the best effect for ${gamma}-PGA$ production. A $2^{6-2}$ fractional factorial design was used to screen factors that influence ${gamma}-PGA$ production significantly, and a central composite design was finally adopted to formulate the optimal medium. ${gamma}-PGA$ productivity improved approximately 2-fold when the optimal medium was used compared with the original nonoptimized medium, and volumetric productivity reached a maximum of 58.2 g/L after a 24-h cultivation period.