This study is to analyze the stress and displacement on the jaws during the bilateral and unilateral clenching task on three dimensional finite element model of the dentated skull. For this study, the computed tomography(G.E.8800 Quick, USA) was used to scan the total length of human skull in the frontal plane at 1.9mm intervals. The CAD data were extracted from the tomograms through digitizer(Summa Sketch III, USA) and then reconstructed by means of the spline method in the CAD program. In this project, a commercial software I-DEAS(Master Series ver-sion 3.0, SDRC Inc, USA) was used for three-dimensional stress analysis on the finite element model. which consists of articular disc, maxilla, mandible, teeth, periodontal ligament and cranium. The results are as follows. ; 1. During the bilateral clenching, each major muscle forces caused high stresses on various areas of skull: masseter muscle on articular disc and teeth ; temporal muscle on mandible and periodontal ligament ; medial pterygoid muscle on the temporomandibular joint. During the unilateral clenching, masseter muscle induced the maximum stress ; medial pterygoid muscle the minimum stress. 2. During the bilateral clenching, higher compressive stresses on articular disc were generated by the masseter muscle and higher deformation occurred on the most front outer sites. And during the unilateral clenching, temporal muscle and medial pterygoid muscle exerted their forces to twist temporomandibular joint area of the balancing side and induced a higher compressive stresses on the front outer sites of articular disc. 3. During the bilateral clenching, the masseter muscle bended the mandible outwardly, and then caused tensile stresses on the lingual surface of mandibular symphysis. And the medial pterygoid muscle caused tensile stresses on the labial surface of mandibular symphysis. 4. When each muscles were simultaneously applied on jaws, a high stress and displacement took place on mandible rather than on the maxilla. Also, a high stress and displacement took place during the unilateral clenching rather than during the bilateral clenching.