The objective of this study was to evaluate the effects of inorganic phosphorus source and phytase addition on performance, nutrient digestibility and bone mineralization in broiler chickens. In Exp.1,150 two-day old, male broiler chicks were fed a corn-soybean meal basal diet supplemented with phosphorus provided by dicalcium phosphate, tricalcium phosphate or defluorinated rock phosphate. Five cages containing 10 birds were allotted to each of the three treatments. In Exp. 2,120 three-day old, male broiler chicks were fed the basal diet from Exp. 1 supplemented with 0,250,500 ,or 1,000 FTU phytase per kg of diet. Six cages containing five chicks were allotted to each of the four treatments. In Exp. 1, there was no difference in weight gain, feed intake or feed conversion as a result of feeding the different sources of inorganic phosphorus. The digestibility of phosphorus was significantly lower ( P =0.01 ) for chicks fed diets supplemented with tricalcium phosphate than for chicks fed the other two diets. However, despite the lower digestibility, serum phosphorus levels did not differ among the three treatments. For Exp. 2, feed conversion showed a linear improvement (P = 0.03 )with increasing levels of phytase inclusion ( days 0 to 33 ). Phytase supplementation resulted in linear increases in the digestibility of dry matter ( P = 0.02 ),crude protein ( P = 0.04 ) and energy ( P ＜ 0.01 ).Chicks fed 1,000 FTU/kg phytase had significantly higher bone calcium ( P = 0.05 ) and bone breaking strength (P = 0.04) than chicks fed the basal diet on day 33. In conclusion, the results of the current study indicated that the performance of birds fed diets supplemented with dicalcium phosphate, tricalcium phosphate or defluorinated phosphate was similar and therefore production costs could be lowered by choosing the cheapest inorganic phosphorus source when formulating diets for poultry. When diets were formulated to meet dietary phosphorus requirements, the growth of broilers was not enhanced with phytase supplementation. However, increases in feed conversion and bone breaking strength and its potential to impact culling and mortality in broiler operations may be sufficient justification for the routine inclusion of phytase in diets fed to broilers.