Fibromatosis or desmoid tumor is a rare, benign, slow-growing fibroblastic neoplasm originating from musculo-aponeurotic stromal elements. Clinically fibromatosis might mimic other malignant tumors, such as breast carcinoma. Although this benign tumor has no metastatic potential, it can be locally aggressive and have frequent recurrences. Although the etiology is unknown, it might be associated with trauma and genetic disorders. Herein, we report on a rare case of fibromatosis of breast of desmoid type. To our knowledge, this the first case in Korean dermatologic literature. A 43-year-old female presented with an asymptomatic, two, 0.5 cm-sized, palpable, irregular-shaped, erythematous nodules on the left breast for 3 years. The patient denied nipple discharge or changes in the breast contour. She had no history of trauma, or breast related-procedures. She had no past or family history of malignancy. Ultra-sonogram demonstrated two, 2.2 cm and 0.6 cm-sized, dermal nodules at the left 4 and 10 o``clock direction, respectively. Histopathological examination showed a proliferation of spindle cells and collagen deposition, which was consistent with fibromatosis of breast. Immuno-histochemical staining revealed a negative reaction to β-catenin. We recommended a wide excision, but the patient refused