Abstract: For separating γ- PGA without any alcohol, a extractive method was developed to separate and purifyγ- PGA from culture broth. The culture broth was filtrated with diatomite to remove cells, and the macromolecular polysaccharide was catabolized by enzymolysis.Then, active carbon was added as decoloring agent and the small molecular weight impurity was removed by ultrafiltration.Finally, purified γ- PGA was obtained by lyophilization.The optimum quantity of using mixed diatomite loading ( ratio of coarse to small diatomite 2∶1) was 1.5% ( w / v) and over97% of cells were removed from γ- PGA broth.The optimum conditions of decoloration were as follows: the addition of active carbon 1.5% ( w / v) , temperature 30℃, p H5, processing time 60 min. The optimum membrane module of ultrafiltration was 10 ku and the concentration rate of ultrafiltration was 9: 1. The purity of γ- PGA was 90% after lyophilization for 18 h.The study of separation and purification of poly- γ- glutamtic acid without any organic solvents was imperative and it provided an important basis for Industrial production of γ- PGA.