A 40-week feeding trial was conducted to demonstrate the effects of different dietary levels of available phosphorus (0.12, 0.22, and 0.45%) and Escherichia coli derived phytase (ECP) supplementation with 100, 150 and 250 FTU/kg of the lowest available phosphorus (aP) diet on the long term performance of 192 laying hens from 20-60 weeks of age. The phytase activity (Pichia pastoris) of ECP was 2000 FTU/g. One unit of phytase (FTU) from Pichia pastoris was defined as the amount of enzyme required to release 1 μmol of inorganic phosphate (iP) per unit from sodium phytate at 37°C and pH 5.5. Hens fed with deficient aP diet (0.12% AP) without phytase supplement or additional iP had decreased hen-day egg production (P<0.05) and lower average daily feed intake (P<0.05). The negative impact of low aP diet on egg production was less in hens 53 weeks of age and older. For the overall period, ECP supplementation to aP deficient diets improved hen day egg production (P=0.06), feed intake (P<0.05), feed conversion ratio (P<0.05) and feed efficiency P=0.07) of layers. Overall, the addition of 0.10% iP to aP deficient diet only improved feed intake (P<0.05) and tends to improve feed conversion ratio (P=0.08). Based on the results, supplementing ECP with 100- 150 FTU/kg or 50-75 g/metric ton inclusion rate to a laying hen diet containing 0.12% aP will be sufficient to recover the suppressive impact of aP deficiency in commercial laying hens.