A case of ductal adenoma of the breast in a 66-year-old woman is reported. The lesion was a small, firm nodule present in the periareolar area of the left breast. It showed extensive hyalinization with tubular structures and spotty calcifications. In spite of such a regressive and relatively well-circumscript appearance, focal eccentric peripheral sclerosis with distorted ductal structures suggested malignancy. However, immunohistochemical examination demonstrated a preserved myoepithelial layer surrounding the ducts. The tumor also showed focal chondromyxoid change and adipocytic differentiation. The myxoid change started exclusively around the ductal structures within the hyalinized acellular stroma and coalesced to form larger chondromyxoid areas. Myoepithelial cells constituting the ductal elements may have been responsible for the aberrant mesenchymal differentiation of this tumor.