Hamartoma of the breast is rarely found, but its characteristic mammographic appearance has been previously described. We present a case to reviw the clinical, mammographic, and pathologic features of this unusual entity. A 40-year-old woman visited to our hospital with the chief complaint of a lump in her left breast. Mammography showed an encapsulated tumor consisting of fatty tissues interspersed with areas of density similar to normal glandular tissues. The tumor was surgically enucleated, and the histology showed to be a hamartoma. The breast hamartomas are rare and only nine cases have been reported in Japan. With a widespred use of mammography, our chances to encounter the tumor will be increased.