The present invention relates to isolated polypeptides having phytase activity and isolated polynucleotides encoding the polypeptides. The polypeptides are related to a phytase derived from Hafnia alvei, the amino acid sequence of which is shown in the appended sequence listing as SEQ ID NO: 10. The invention also relates to nucleic acid constructs, vectors, and host cells comprising the polynucleotides as well as methods for producing and using the polypeptides, in particular within animal feed.