Multinucleated giant cells of osteoclast-like appearance can be seen in a type of anaplastic carcinoma of thyroid and only a few case reports for fine needle aspiration cytologic findings are found in the literatures. Recently, we experienced a case of anaplastic carcinoma of thyroid with many osteoclast-like giant cells in a 72-year-old woman. The cytologic features and immunohistochemical results are described with special emphasis on differential diagnosis.