For the complete cure of oral cancer suspected to have invaded the mandible in clinical & radiological evaluation, the mandible resection in planned. The aim of this clinical study was to help in decision making in the method & the extent of the mandibular resection surgery. This study was conducted on 46 oral cancer patients, who received cancer surgery including mandibulectomy. And we evaluated the relationship between the pathologic results of resected mandible and the location, size and clinical newk node involvement, tumor cell differentiation. The results are that ; (1) Hiher incidence of bone invasion patterns were observed in tumor of mouth floor & gingiva compared to those of tongue & tonsil, and (2) No significant relationship was found between bone invasion of tumor and tumor size, neck node involvement tumor cell differentiation. The approximation between tumor and bone seems to be the most reliable factor among the other factors in decision making of mandibular resection.