The aim of this study is to examine the relationship between the degree of gingival curvature in labial gingival margin of lower incisors and the gingival recession in patients with mandibular prognathism after orthognathic surgery. And then the effect of these anatomical feature of periodontal tissue to gingival recession were evaluated and compared with change of mandibular incisor inclination and genioplasty which were known as the factors of gingival recession. The pre-treatment lateral cephalograms and lateral cephalograms taken just before surgery and dental casts of 32 skeletal Class III malocclusion patients were collected. The change of inclination of mandibular incisors was estimated in the lateral cephalograms on the basis of mandibular plane and we defined the increase of clinical crown length of the lower incisors after orthognathic surgery as the amount of gingival recession. The relationship between gingival curvature, change of mandibular incisor inclination and gingival recession was evaluated by Spearman correlation analysis. And the difference of gingival recession between genioplasty group and non-genioplasty group was evaluated by T-test. Based on the result, the patients who have more prominent gingival curvature in lower incisors showed more gingival recession after orthognathic surgery and there was no relationship between the forward change of mandibular incisor inclination and gingival recession in patients with mandibular prognathism. And we concluded that genioplasty could be the cause of gingival recession in patients with mandibular prognathism after orthognathic surgery.