The current work was planed out to clarify the effect of thyroxine adminstration on regulation of calcium, inorganic phosphorus and magnesium levels in blood and bone. A total of 20 mature rats were utilized and divided into two groups; treated and control groups. Thyroxine was given to rats of treated group for one month. The results showed a higher calcium level in blood of treated group. Moreover, the levels of the three tested elements were significantly higher in bone ash of treated group. It can be concluded that thyroxine has a role in the regulation of calcium level in blood and deposition of calcium, phosphorus and mag nesium in bone.