An experiment was conducted to determinate the effect of microbial phytase supplementation on broiler chickens blood performance (calcium, phosphorus, magnesium), using 300 day-old commercial broiler chickens Cobb 500 from 1 to 42 days of age. The aim of study was the monitoring and mathematic-statistical evaluating of the effect of microbial phytase (0.1%) in feed mixtures with different content of total phosphorus (control group 4.5% of phosphorus, trial group 2.3% of phosphorus, trial group 2.3% of phosphorus + phytase 0.1%). The biochemical values of blood coefficients were evaluated by automatic clinical analyzer Microlab 300. The values of phosphorus, calcium and magnesium content in the blood of broilers were not statistically significant (P>0.05). In addition we concluded that phytase supplementation to the feed mixtures did not influence calcium, phosphorus and magnesium content in the blood of broiler chickens.