The authors experienced a case of malignant mesenchymoma of the liver in a 6-year-old girl The patient is perfectly well without any evidence of recurrence or metastasis 14 months after undergoing right trisegmentectomy af the liver. This case is unique in that the tumor has the components of mesenchymal hamartoma intermixed with undifferentiated sarcomatous elements. The histologic findings in the present case seem to provide a clue that may substantiate the contention that malignant mesenchymoma arise from malignant transformation of mesen- chymal hamartoma.