BACKGROUND: Mucocele-like tumor(MLT)is a rare benign condition, and ofter misdiagnosed as mucinous carcinoma. METHODS: We encountered a 31-year-old woman with MLT of the breast. The patient presented with an elastic hard mass, 0.5cm in diameter, located in the upper outer quadrant of the right breast. RESULTS: Physical examination as well as ultrasonography and mammography indicated a benign lesion. However, mucinous carcinoma was suspected based on aspiration biopsy cytology. MLT was finally diagnosed on excisional biopsy. CONCLUSION: Awareness of this breast disease helps to prevent misdiagnosis and unnecessary surgery.