The giant cell tumor of thyroid which resembles osteoclastoma is assumed a rare type of anaplastic thyroid cancers. Female patient of .45 years old, is f olio wed f or 4 years by the diagnosis of warmtnyroid nodul and sent to our clinic when the nodul appeared inactive. Frozen section is applied during surgery, left total and right subtotal resection is performed. In the hystopathological examination, osteoclastic giant cell tumor which grew on the basis of folicular carcinoma, is diagnosed. The place of these cases, which show hytopathological structural changes beside malignant potential, among the thyroid tumors is discussed under the light of literature.