The present invention relates to a novel phytase enzyme, a novel isolated nucleic acid molecule coding the enzyme, and a novel Yersinia intermedia having phytase activity. Particularly, the present invention relates to the phytase having (a) Theoretical molecular weight 45.5 kDa, (b) high specific activity 3960±248 U/mg, (c) high stability at high temperature and wide pH, (d) optimal pH of 4.0-5.0, (e) optimal temperature of 50-60°C, (f) high resistance to pepsin and trypsin. The phytase is very suitable to be used in feed of monogastrics as feed additive. The present invention also relates to a recombinant vector comprising said nucleic acid molecule, a recombinant host cell (e.g., Pichia pastoris ) harboring said recombinant vector, and a method for producing phytase using the recombinant host cell. The present invention further provides a feed additive comprising said phytase and/or host cells expressing a phytase as effective ingredient. In addition, the present invention provides a novel method for isolating phytase from a target organism.