γ-Polyglutamic acid (γ-PGA) is an anionic natural polymer, which is widely used in many fields.In order to explore the possibility of using γ-PGA with different molecular weight as a potential cosmetic whitening agent, γ-PGA was prepared by microbial fermentation with Bacillus subtilis as producing strain, and five groups of γ-PGA with different molecular weight were prepared by chemical degradation.Taking the inhibition rate of intracellular and extracellular tyrosinase activity as an index, the tyrosinase inhibitory activity of five groups of γ-PGA with different molecular weight was studied.The results showed that γ-PGA with molecular weight of 21, 117, 282, 432 and 501 kDa was obtained at 90 ℃ and pH 3.0.The determination of enzyme kinetic function by enzyme labeling instrument showed that all the five groups of molecular weight γ-PGA could inhibit tyrosinase activity, and the inhibition rate of extracellular tyrosinase activity increased with the increase of molecular weight, which preliminarily verified the tyrosinase inhibition activity of γ-PGA with different molecular weight.