Leiomyoma of the nipple is a rare, benign, non-epithelial tumor that is thought to arise from smooth muscle fibers in the subareolar tissue of the breast. We report an unusual case of leiomyoma of the nipple in a 32-year-old woman in whom the diagnosis was made by ultrasound-guided core needle biopsy. She came to our hospital complaining of a recently enlarged nipple with discharge and erosion in the region of the left nipple-areolar complex. This mass was evaluated by mammography, ultrasonography, and magnetic resonance imaging (MRI). To the best of our knowledge, this is the first case of a leiomyoma of the nipple examined by MRI. MRI showed an oval mass with circumscribed margins that appeared as an intermediate signal intensity on both T1- and T2-weighted images. A dynamic MRI study showed a rim-enhancing oval mass with delayed persistent enhancement. Ultrasound-guided core needle biopsy revealed spindle cell proliferation consistent with leiomyoma of the nipple.