The experiment was carried out on Hisex Brown hens aged 26-48 weeks divided into 12 groups of 18 birds kept in single cages. Layers were fed wheat-maize-soyabean meal diets containing 0.50, 0.55 and 0.60% total phosphorus (TP), 0.25, 0.30 and 0.35% available phosphorus (AP) supplemented with 0, 150, 300 or 450 units of microbial phytase (FTU) per kg. Hens were fed diet containing 0.50% TP supplemented with 300 FTU showed the highest laying rate (93%) and good egg shell quality. However, the thickest egg shells and the highest breaking strenght were found when diets containing 0.30-0.35% AP were supplemented with 150 FTU. Hens fed diet with 0.25% AP + 300 FTU excreted 100 mg/day/hen less P than those fed diet with 0.35% AP (0.60% TP), not supplemented with phytase. As the optimal levels in the diet are considered 0.25% AP + 300 FTU or 0.30% AP + 150 FTU.