The purpose of this study was to evaluate the morphology of mandibular symphysis and location of lower incisor under the influence of the craniofacial skeleton in skeletal Class III malocclusion. The sample consisted of 132 adults who, have severe Class III malocclusion(prognathism group, 33 males and 33 females), and who have normal occlusion(normal group, 33 males and 33 females). They had not received any orthodontic treatment or orthognathic surgery. The, lateral cephalograms were evaluated. The results were as follows : 1. Prognathism group were larger than normal group in comparison of facial skeleton (p<0.05) with the exception of ∠FH-Pal, ∠SNA. 2. In the morphology of symphysis, measurements of anteroposterior width(LaABBW, LiABBW, SW) of prognathism group were significantly less than that of normal group(p<0.001). 3. In the correlative analysis between the craniofacial skeleton and symphysis measurements of prognathism group, vertical measurements in relation with cranial base and mandibular plane showed reverse correlationship with anteroposterior width of symphysis(LiACBW, LaACBW, LiABBW, SW)(p<0.05). But, there was not distinct difference between horizontal skeletal measurements and symphysis measurements(p>0.05). 4. The probability by regression test between vertical measurements(∠SN-Mn, ∠FMA, ∠Pal-Mn, ∠LFH) and symphysis measurements(LiACBW, LiABBW, SW, ∠LISA) were very high(p<0.001).