Objective: The aim of the study was to report a case with a giant phyllodes tumor of the left breast and discuss the diagnostic and management challenges. Methods: A 47-year-old female patient was admitted to our center (Department of General Surgery, the First Affiliated Hospital, Luzhou Medical College, China) due to a large left breast mass for about 2.5 years. Core tissue biopsy showed mixed epithelial-stromal proliferation suggestive of a phyllodes tumor. Left modified radical mastectomy with dissection of level I and level II lymph nodes was performed. Results: The pathologic findings of this procedure were consistent with borderline phyllodes tumor. The tumor measured 47.5 cm × 37.0 cm × 28.0 cm and weighed 9.79 kg ex vivo. Conclusion: To our knowledge, this patient presented one of the biggest phyllodes tumors of breast in all cases reported in English-language publications so far. Objective: The aim of the study was to report a case with a giant phyllodes tumor of the left breast and discuss the diagnostic and management challenges. Methods: A 47-year-old female patient admitted to our center (Department of General Surgery, the First Affiliated Hospital, Luzhou Medical College, China) due to a large left breast mass for about 2.5 years. Core tissue biopsy showed mixed epithelial-stromal proliferation suggestive of a phyllodes tumor. Left modified radical mastectomy with dissection of level I and level II lymph node was performed. Results: The pathologic findings of this procedure were consistent with borderline phyllodes tumor. The tumor measured 47.5 cm × 37.0 cm × 28.0 cm and weighed 9.79 kg ex vivo. Conclusion: To our knowledge, this patient presented one of the the biggest phyllodes tumors of breast in all cases reported in English-language publications so far.