Poly (γ-glutamic acid) (γ-PGA) is a special anionic, water-soluble and high viscous polymer  which is condensed by glutamate via amide linkages between their a-amino and γ-carboxylic acid groups . For its excellent characters, potential applications of γ-PGA have been of interest in the past few years in a broad range of industrial ﬁelds . And the decision to application of γ-PGA will be done, depending on its’ molecular weight. So this article main expresses the influence of different carbon sources to γ-PGA’s molecular weight distribution. By SDS-PAGE, we found that the molecular weight distributions of biosynthetic γ-PGA were different in the different carbon sources. All the results showed that changing the carbon source of mediums did make the biosynthetic γ-PGA’s yield and molecular weight distribution been changed.