Tongue posture at rest position of Class III malocclusion is very important in malocclusion and phonation. Because Class III malocclusion shows low tongue position, speech defect is commonly occured. This study was attempted to evaluate the correlationship between the tongue posture at rest position and during /s/ phonation and facial skeleton in centric occlusion. Thirty subjects with Class III malocclusion who had no orofacial defects such as cleft palate, medical history of neurologic pathology, hearing defect and any previous speech therapy were selected. Ninety sheets of lateral cephalometric radiographs taken at rest position, during /s/ phonation and centric occlusion were traced, measured and statistically analysed. The results obtained were as follows; 1. In Class III malocclusion, the posture of tongue was positively correlated with the position of hyoid body. The hyoid body was positioned anteriorly and inferiorly as the vertical facial skeleton was increased in centric occlusion. 2. In Class III malocclusion, the vertical position of tongue tip at rest position was not correlated with facial skeleton in centric occlusion, but the horizontal position had low correlation with mandibular body length, APDI, and 1 to SN. 3. In Class III malocclusion, there was the tendency that the dorsal position of the tongue was lowered as the vertical facial skeleton was increased. 4. In Class III malocclusion, the vertical and horizontal position of tongue tip during /s/ phonation was not correlated with facial skeleton in centric occlusion.