An experiment was conducted using day-old Hub- bard ®broilers in order to study the effect of microbial phytase on the performance of broilers in a commercial farm for 39 days. The control diet adequate in non-phytate phosphorus (0.5%) was fed to one house with 14751 birds. The experimental diet (low in non-phytate phosphorus 0.4%) was fed to another house of 15345 birds after being modified using the matrix values for Ronozyme® P CT (phytase). Parameters measured included body weight gain, feed conversion, mortality, profit per bird, tibia ash (total ash, calcium, phosphorus, magnesium and zinc percent ages), serum calcium, phosphorus, alkaline phosphatase as well as fecal calcium and phosphorus output. Phytase supplementation (750 U/kg) to the low non-phytate phosphorus diet significantly improved body weight gain. Phytase supplemented birds consumed more feed than the non-supplemented ones but feed conversion was not different between the two groups as well as mortality %. However, phytase supplementation significantly (P<0.01) increased serum calcium and phosphorus levels and reduced alkaline phosphatase. Furthermore, phytase supplementation significantly increased tibia weight, length and zinc content but had no effect on tibia total ash. calcium, phosphorus or magnesium content. Fe- cal calcium and phosphorus output was significantly (P<0.01) reduced by 32.9% and 27.9% respectively in the phytase-supplemented group Results suggest that dietary phosphorus can be reduced without seriously affecting the skeleton of broilers and that phytase would have other benefits by reducing the cost of the diet as well as improving birds live weight gain, in addition to reducing environmental pollution as manifested by reduced fecal phosphorus output.