We describe the successful treatment with octreotide, a somatostatin analogue, of a patient with malignant hypercalcemia associated with advanced breast cancer. A 70-year-old female with advanced breast cancer was admitted to our department for treatment of hypercalcemia. The administration of pamidronate disodium was effective to decrease serum calcium from 6.2 mEq/l to 4.0 mEq/l for the first time, but her hypercalcemia later responded less to pamidronate, and her serum calcium remained raised in spite of the administration of pamidronate and elcatonin. Then, her condition deteriorated with hypercalcemic symptoms, such as nausea vomiting and drowsiness. After octreotide treatment (100 microg/body/day, s.c.) with a combination of prednisolone, her serum calcium level improved from 6.7 mEq/l to 5.0-5.5 mEq/l, Leading to a dramatic improvement in her symptoms. During these treatments, anti-cancer therapy, hydration and the administration of diuretics have been continued. We think octreotide is very useful for the treatment of malignant hypercalcemia associated with advanced breast cancer.