The antioxidant activities such as reducing power,Fe2+ chelating activity,DPPH·radical scavenging activity,ABTS·+ scavenging activity,and hydroxyl radical-scavenging activity of crayfish(Procambarus clarkii) shell protein hydrolysate(CSPH) prepared with Protamex were evaluated.The radical scavenging activity,reducing power and Fe2+ chelating activity of CSPH increased with its increasing concentration.The Fe2+ chelating activity was fixed when its concentration reached 10 mg/ml.The molecular weight distribution of CSPH revealed that 92.79% of the total amount was peptides with molecular weight lower than 1 000 u,composing mostly of low molecular weight peptides lower than 180 u(21.50%),from 180 to 500 u(50.51%),and from 500 to 1 000 u(20.15%).