Non-ruminant animals do not synthesize phytase enzyme, a substance capable to act on phytate molecule to liberate phosphorus. The non-available phosphorus pass through the digestive system of the non-ruminants practically without being digested and the inclusion of inorganic phosphorus sources in diets of those animals is necessary. The use of phytase enzyme in rations for pigs can contribute to the elimination or reduction of the use of inorganic phosphorus sources and reducing the environmental impact caused by the excretion of this mineral. The experiment was designed to evaluate the biological phosphorus flow in pigs fed with diet containing different phytase levels, using the isotope dilution technique.