Objectives To heterologously express peanut ( Arachis ipaensis ) Bowman-Birk inhibitor (BBI) and characterize its properties. Results A putative BBI gene from peanut was overexpressed in Pichia pastoris with the maximal yield of 11.1 mg/L in a 250-mL shaking flask fermentation. The recombinant peanut BBI (rPBBI) was purified and its molecular weight was estimated to be 9 kDa. Purified rPBBI showed 5223.6 TIA/mg inhibitory activity toward trypsin. It retained more than 95% of its inhibitory activity over wide range of temperatures (40 to 90 o C) and pH (2.0 to 10.0) after incubation for 60 min. When presence of 100 mM dithiothreitol, rPBBI lost more than 80% inhibitory activity in 30 min. Conclusion The current investigation expressed a peanut BBI with stable inhibitory activity against trypsin and exposed the potential of heterologous overexpression approach in large scale production of BBI.