The isolation and purification of acid protease in Pleurotus cornucopiae(Pers.) Rolland were performed using DEAE-Sephadex A-50, CM-Cellulose, DEAF-Cellulose and Sephadex G-75. Three kind of unknonown proteins are detected. The property of this enzyme was as follows. 1) When bovine serum albumin was employed as a substrate for this enzyme, protein fraction(I) among three unknown protein above showed the following properties. Km was 0.20 mM; Vmax., 21.8 nM/min; optimum temperature 50℃. 2) The activity of enzyme was inhibited by Ca^(++), Cu^(++), Zn^(++), Fe^(++) and Mg^(++), but stimulated by Co^(++) ion. 3) The enzyme was found to be a monomer which consists of 15 different amino acids. The molecular weight was determined to be approximately 56,000.