This article studies the anatomy of the posterior maxilla pertaining to bone-cut design of Le Fort I osteotomy to avoid the injury to the descending palatine artery in Thais. Fifty-five skulls (38 males, 17 females) were assessed for the anatomical landmarks by a combination of direct inspection, computerized imaging, and computed tomography scan analysis. The results showed that 27.28% of the pterygomaxillary junction (PMJ) became synostosis. The mean heights of the PMJ, posterior maxilla, and maxillary tuberosity were 15.14 +/- 2.46 mm, 22.51 +/- 3.50 mm, and 7.45 +/- 2.76 mm, respectively. The mean length of the medial sinus wall measuring from the piriform rim to the descending palatine canal at the Le Fort I level was 34.40 +/- 2.96 mm. The mean widths of the posterior incision of Le Fort I osteotomy at the maxillary tuberosity and PMJ were 20.38 +/- 2.82 mm and 11.60 +/- 1.57 mm. The mean length of the posterior maxilla was 27.18 +/- 2.49 mm. Distances from the greater palatine foramen to the maxillary tuberosity incision and PMJ incision were 1.76 +/- 1.12 mm and 3.59 +/- 1.40 mm. The mean angle between the descending palatine canal and the hard palate was 57.33 +/- 4.54 degrees . There were no significant differences in any measurements between sides and genders, except the pterygoid process width and posterior maxilla length of males were longer than those of females (P < 0.05). This study could provide better understanding of the posterior maxillary anatomy that is important for the bone-cut design of Le Fort I osteotomy to avoid excessive intraoperative and postoperative hemorrhage including ischemia of the mobilized maxilla.