A 42-year-old woman was presented with an ovoid mass detected on a mammography. Her physical examination revealed a 2 cm ill-defined mass in the right upper outer breast. A sonogram demonstrated a 1.9 cm ovoid, partially microlobulated and partially well-circumscribed, and an isoechoic mass with increased vascularity on Doppler imaging. Surgical excision was performed and the pathology revealed ductal carcinoma in situ (DCIS) in a phyllodes tumor. DCIS within a phyllodes tumor is a very rare event. Here, we report on a case of DCIS in a phyllodes tumor.