The solid state fermentation (SSF) was carried out for the production of poly gamma-glutamate (PGA) from a new strain Bacillus subtilis CCTCC202048. The fermentation factors, which included composition of substrates, initial moisture content, incubation temperature, fermentation period, and additional nutrients such as mineral salts, carbon sources and nitrogen sources, were investigated and optimized. The maximum PGA production (83.61 g/kg of dry substrate) was obtained in the mixed substrates of soybean cake powder and wheat bran (11:9, w/w) supplemented with glutamate (40.14 g/kg), citric acid (18.50 g/kg), NH4NO3 (20.05 g/kg) and mineral salts (MgSO4 center dot 7H(2)O, CaCl2 center dot 2H(2)O, FeCl3 center dot 6H(2)O and MnSO4 center dot H2O), with initial moisture content as 65%, at 40 degrees C incubated for 42 h. This yield was four times more than that before optimization. This is the first report on optimization of PGA production in SSF. (c) 2005 Elsevier Ltd. All rights reserved.