Adenosis tumor is a ra re tumor of the breast and primarily consists of adenosis. Authors report a case of surgically proved adenosis tumor in a 31-year-old woman. Mammogram showed a Iobulated, well-circumscribed mass with several surrounding radiolucent halos. In the center of the mass several linear radiolucent densities were seen with the appearance of a conglomerated well-circumscribed mass such as fibroadenoma. These linear radiolucent densities were consistent with the fat between the fibrous sclerosis in pathologic specimen. Ultrasonogram showed a well-circumscribed mass with homogeneous low echogenicity, partial posterior enhancement, and bilateral acoustic shadowings.