Phyllodes tumor or cystosarcoma phyllodes is a rare disease and is usually seen in middle-aged patients. Ruptured phyllodes tumor is a very rare condition. Our study reports patient presentation, diagnosis method, and treatment of an unusual case. A 58-year-old premenopausal female was diagnosed with a phyllodes tumor and presented with a rapidly growing mass for 2 months that ruptured 1 month later. She underwent simple mastectomy at the left side of her breast and received adjuvant radiotherapy. No recurrence was found 4 months after operation.