The purpose of the presented study was to determine the reaction of hens to low-phosphorus diets and supplementation with different microbial phytases by assessing laying performance, feed intake, egg shell quality, as well as bone strength parameters and bone contents of Ca, P, Mg, and Zn. At the age of 16 weeks, 288 Lohmann Brown pullets were allocated to 6 dietary treatments, each treatment group consisting of 12 cages, 4 birds per cage. Before the laying period the pullets were fed with a standard diet containing 150 g crude protein (CP) 11.3 MJ ME, 4 g available P and 10.6 g of Ca per kg feed. The experimental diets fed from the first day of laying were based on wheat and barley and contained 165 g CP and 11.2 MJ ME/kg. In diets I to V the level of available P was lowered to 1.89 g/kg in the first period of laying and to 1.31 g/kg in second and third periods, while in the control (VI) diet the amount of available P was 3.09 g/kg. In diets II-V two kinds of phytase were applied at levels of 300 or 450 U/kg of diet. The phosphorus level did not affect the laying rate. The higher P level enhanced egg shell thickness. Supplementation with phytase did not affect the performance of hens. Improved feed conversion was noted only when the diet was supplemented with 450 U of phytase B per kg. Phytase supplementation of low-P diets significantly improved the strength and elasticity of the tibia and femur, which in groups II-V were on a similar level as in the positive control group.