Abstract: Provided is an isolated phytase derived from a microorganism. The microorganism is preferably from the genus Monascus. The phytase has a Michaelis constant of 10 to 110 &mgr;M when phytic acid is used as a substrate. A process for producing the phytase is also provided as is an animal feed comprising the phytase. The phytase is preferably isolated from Monascus anka IFO 30873. The phytase has a Km of 107 &mgr;m when phytic acid is used as a substrate, the optimum pH is 2.5, the optimum temperature is 45° C., the molecular weight of the phytase is 140 kDa when measured by gel filtration, and the isolectric point is 5.2 using chromatofocusing.