This cross-sectional study was conducted in order to determineaveolar arch sizes in cephalometric measuments of students with Angle's class II malocclusions of Thai Nguyen University of Medicine and Pharmacy and to compare these of Angle's class II division 1 and division 2. In total of 48 students, 68,7 percent were class II division 1 malocclusions and 31,3 percent were class 11 division 2 malocclusions. Most of maxillary aveolars were in normal position but the mandibulary aveolars were deviation. On the average, Ul-SN values of Cl11/1 (109,15 + or - 11,89) was higher than that of Cl11/2(96,93 + or - 27,46). In addition, the upper incisors and lower incisors of Cl11/1 were generally found in protrusive positions.