Mesenchymal chondrosarcoma of the paranasal sinuses is a rare malignant tumor and has a poor prognosis due to local recurrence and distant metastasis. It has unique and distintive histologic picture, being composed of richly cellular and undifferentiated mesenchymal cells and islands of relatively well differentiated cartilage. The treatment in mesenchymal chondrosarcoma is radical resection, however, chemotherapy and radiation therapy have been reported. The author experienced a case of mesenchymal chondrosarcoma of the paranasal sinuses which occured in 11 year old girl. The patient underwent Lt side total maxillectomy except enoculation.