Background: Addition of the phytase enzyme to the diet of monogastric animals is an effective and practical method for both utilization of phytate-P and P disposal. Besides hydrolytic effects on phytate, phytase may also improve the availability of minerals. Alkaline phosphatase (ALP) plays an important role in bone mineralization. Since dietary P levels decrease, serum ALP level has been shown to increase. It was reported that pigs and broilers fed phytase had lower serum ALP level. The present study aimed to investigate the effect of microbial phytase on serum calcium (Ca), inorganic phosphorus (Pi) levels and ALP activities in broilers fed diets containing different P levels.