Abstract: A putative trypsin inhibitor from Glycine max(namely STI encoded by sti)was expressed in Pichia pastoris and its biochemical characteristics were investigated. Resuts showed that:In shaking-flask fermentation experiments,recombinant yeast GS115(pPIC-STI)secretorily expressed 30 mg/L STI. The recombinant STI retained more than 85% of its maximum inhibitory activity after incubation at 40~80℃ or pH 2.0~11.0 for 1 h. Its activity was significantly enhanced by K⁺,Zn²⁺ and Mg²⁺,but strongly inhibited by Cu²⁺,Mn²⁺,Ca²⁺,Fe²⁺ and Fe³⁺. The STI exerted the strongest,specific and non-competitive inhibitory effects toward trypsin,which indicated that STI was a typical peptide-type trypsin inhibitor. All these distinct biochemical properties make STI a good candidate for food and pharmaceutical applications.