Phosphorus is a necessary nutrient for animal growth, and the lack of phosphorus in livestock/poultry feed will reduce the production performance of livestock and poultry. Plant feed ingredients contain large amount of phosphorus. However, most phosphorus exists in the form of phytate-phosphorus. Due to the lack of endogenous phytase in livestock and poultry, phytate-phosphorus could not be released and absorbed by livestock and poultry. Thus, feed companies have to supplement costly inorganic phosphorus into feeds. Livestock and poultry fed with feeds supplemented with inorganic phosphorus release most phytate-phosphorus and unabsorbed inorganic phosphorus into the environment through excreta, causing more and more serious environmental pollution. The addition of exogenous commercial phytase into livestock/poultry feeds can efficiently utilize phytate-phosphorus thus minimize environmental pollution. Phytase as an enzyme is capable of breaking down phytates in feeds to release inorganic phosphorus and inositol as well as protein, amino acids, trace minerals and other nutrients chelated with phytates. Thus, phytase can reduce or eliminate the supplement of inorganic phosphorus in feeds for monogastric animals and improve the utilization efficiency of these nutrients contained in feedstuff. Phytase has been widely used in feed industry. The number of large and medium feed companies, which use phytase in livestock and poultry feeds, exceeds 2,000 in China and 5,000 in the world, with an annual growing rate of more than 20%. Many researches and case studies have demonstrated the following benefits of phytase: 1) Reduce the supplement of costly inorganic phosphorus in feeds, reduce the feed cost, and increase the profit of both feed companies and farms. The supplement of phytase can increase the utilization efficiency of phytate- phosphorus by 20-40% in pig feeds and 35-58% in chicken and duck feeds 2) Reduce the total phosphorus content in livestock/poultry feeds, and reduce the excreted phosphorus through manure by 40-60%, thus reducing environmental pollution 3) Increases the utilization efficiency of minerals, protein and other nutrients, and improves the production performance of livestock/poultry