When pepsin was used at a concentration of 8 mglml for hydrolysis of 0.02% casein, inhibitory activity of this inhibitor was proportional to a inhibitor concentration of 20 ${mu}g$/ml, and fifty percent inhibition ($IC_{50}$) was observed to be 15 ${mu}g$/ml. The inhibitor was pH-stable at pH range of 5-9 at $100^{circ}C$ for 10 minutes and thermo-stable at pH 7.0 at $100^{circ}C$ to give 100% activity for 20 minutes. The formation of pepsin-inhibitor complex was confirmed by sephadex 6-25 gel filtration and type of inhibition was determined as non-competitive inhibition by Lineweaver-Burk plot. The inhibitor strongly inhibited acid proteases such as pepsin and renin, and it was soluble in methanol very well. On TLC analysis of silicagel 60 using various sohent systems, the inhibitor gave a single spot at Rf range 0.4-0.6. From the result of IR spectrum and color reaction (Rydon-Smith, Biuret), this inhibitor was considered as peptide substance. Melting point and elemental contents were 220-$230^{circ}C$, and C 50.61%-H 8.02%-N 9.34% (found), respectively.