Ultrasonography detected apparent echoes of especially coarse calcifications in a case of mucinous carcinoma of the breast. A 47 year-old female visited this institution with a mass of increasing size in her right breast for 1 year. The ultrasonogram showed two mass lesions: a primary lesion 3 cm in diameter with a margin partially obscured by coarse calcification echoes, and a daughter lesion 1 cm in diameter near the nipple that accompanied no calcification echo. Mammogram of the right breast showed a group of coarse, amorphous calcifications, and MRI depicted both the main and daughter tumor. Mastectomy was carried out when fine-needle aspiration cytologic examination of the primary tumor led to a diagnosis of class V mucinous carcinoma. Both lesions were diagnosed as mucinous carcinomas on histologic examination, and coarse calcifications were found in and around the main tumor. Mucinous carcinomas with coarse calcifications have been rarely reported. Definite diagnosis of breast tumors with coarse calcification echoes on ultrasonogram requires further examination.