Abstract: This study obtained a novel acidi protease gene by cloning, and it was expressed in Pichia pastoris KM71, then the enzymatic properties of this recombinant yeast acid protease rPrA were studied after being concentrated. Besides, its degree of hydrolysis to soy protein isolate (SPI) and casein was initially researched. The results showed that the molecular weight of heterologous expression of recombinant P. pastoris acid protease was about 44 kuand it could get the highest enzyme yield of 46.92 U/mL under the fermentation condition of pH 3.0. The optimum pH for the acidi protease was 3.0, the optimum temperature for rPrA was 35. Although Mn2+ had an active role in its activity, a variety of metal ions could inhibit its activity. 0.1 mmol/L pepstain A could completely inhibit its activity, proving that rPrA had aspartic acid residues in its active site. The hydrolysis to SPI and casein experiment showed that, when E/S was 4 000 U/g, its hydrolysis degrees to SPI and casein were 9.0% and 8.34%, respectively. The results indicated that by optimizing fermentation conditions and functioning with other proteases, rPrA would have a great utility potential in protein hydrolysis, and it was expected in apply to the feed processing industry.