The solid state fermentation (SSF) was carried out for the production of poly g-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 (83.61g/kg of dry substrate) was obtained in the mixed substrates of soybean cake powder and wheat bran (11:9, w/w) supplemented with glutamate (40.14g/kg), citric acid (18.50g/kg), NH4NO3 (20.05g/kg) and mineral salts (MgSO4 7H2O, CaCl2 2H2O, FeCl3 6H2O and MnSO4 H2O), with initial moisture content as 65%, at 40 8C 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.