The objective of this experiment is to investigate roles of calcitonin on urinary calcium and phosphorus excretion in sheep. Three thyroidectomized wethers were injected with 0 (vehicle), 0.25, 0.5 and 1 U/kg body weight of porcine calcitonin and three sham operated sheep were injected with vehicle. Serum calcium and phosphorus concentrations were decreased by calcitonin administration. And serum parathyroid hormone concentration was increased along with the reduction of serum calcium concentration. Urinary volume was more in thyroidectomized sheep than in sham operated ones and tended to be decreased by calcitonin administration though the reduction of urinary volume was not dose dependent. Urinary calcium excretion was more in thyroidectomized sheep than in sham operated ones. Though the smallest does of calcitonin decreased calcium excretion in urine, the largest dose increased urinary calcium excretion in thyroidectomized sheep. Urinary phosphorus excretion was much less in thyroidectomized animals than in sham operated ones. Calcitonin administration increased phosphorus excretion in dose dependent manner in thyroidectomized sheep. However any doses of calcitonin could not recover phosphorus excretion to the level of sham operated sheep. These results suggested that calcitonin commonly decreased urinary calcium excretion for the conservation of calcium, while a high concentration of blood calcitonin increased urinary calcium excretion which promotes the hypocalcemic action of calcitonin. And it was confirmed that calcitonin had a hyperphosphaturic action in sheep.