Background: The morphological characteristics of the alveolar bone thickness between the maxillary sinus and root ca nal tips of the premolars and molars is important for dental implant and orthodontic treatment. The hypotheses formulated were that there would be differences in the morphological characteristics of the alveolar bone at various tooth positions in the posterior maxilla and that age and sex would not influence the findings. This study may provide useful information for dental implant and mini-implant treatment, so as to help lead to successful treatment outcomes. Aim: To evaluate the vertical relationship between the maxillary sinus and molar teeth using cone beam computed to mography (CBCT). Materials and Methods: The study design was retrospective study. We selected 30 CBCT images that were taken in the Central Dental Hospital, Mongolian National University Medical Sciences (MNUMS), between 2021 and 2023. We collected all images according to the inclusion and exclusion criteria. We used Full CBCT (16cm*8cm) images using the target sampling method. The all CBCT images (85kW, 7mA) were obtained with HDX, WILL (DENTRI, Seoul, Korea) using OnDemand3D (CyberMed. Seoul. Korea). The vertical relationship between the maxillary sinus and the maxillary molars was classified into 5 categories according to Kwak’s classification. The study was approved by the Research Ethics Committee of MNUMS. Statistical analyses were done by IBM SPSS version 27 software. Results: A total of 202 maxillary premolars and molars were examined using CBCT images, and were taken in 30 pa tients. The patient group consisted of 12 men and 18 women with an average age of 26.87 years (range, 16–42 years). In the maxillary first premolars: Class I was 77.4%, Class II was 13.2%, Class V was 9.4%, Classes III and IV were not observed. In the maxillary second premolars: Class I was 44.8%, Class V was 37.9%, Class II was 17.2%. In the maxillary f irst molars: Class V was 62.3%, Class I was 24.4%, Class II was 6.7%, Class III was 4.4%, Class IV was 2.2%. In the maxillary second molars: Class V was 63.1%, Class I was 23.9%, Class II was 6.5%, Class III was 6.5%. When examining the distance from the apex of the root of the molars to the floor of the maxillary sinus, the distance between the root of the buccal side of the second molar was the smallest, 0.67±1.36mm, and the distance between the root of the first premolar was the furthest, 5.14±4.32mm (p<0.01). Conclusion Among the maxillary posterior teeth, the second molar was positioned closest to the floor of the maxillary si nus, whereas the first premolar was located at the greatest distance. Regarding the maxillary molars, Type V characterized by root protrusion into the floor of the maxillary sinus was the most frequently observed configuration. Conversely, for the premolars, Type I defined by a distinct separation from the sinus floor was the predominant anatomical relationship.