Recently, mini-implant is popular in the orthodontic treatmentdue to its simplicity and convenient surgical procedure.The objective of this study is to provide the anatomicalguideline for mini-implant placement by analysing thecortical bone thickness in Korean. Hemi-sections of sixteenmaxillae and twenty-two mandibles with normal teeth wereused. Interdental areas between the 1st premolar and the2nd premolar (Group 1), the 2nd premolar and the 1st molar(Gruop 2), and the 1st molar and the 2nd molar (Group 3)were sectioned and then scanned. After setting the axis ofteeth, the cortical bone thickness was measured at thedistance of 2 mm, 4mm, 6 mm, and 8 mm from alveolarcrest. The mean thickness of cortical bone in the maxillaaccording to distance from alveolar crest was 1.30 ± 0.63 mm(2 mm), 1.49 ± 0.62 mm (4mm), 1.72 ± 0.64 mm (6mm), and1.90 ± 0.90 mm (8 mm) at the buccal side and 1.33 ± 0.47mm, 1.31 ± 0.45 mm, 1.37 ± 0.55 mm, and 1.39 ± 0.58 mmat the palatal side. In the mandible, that was 3.14 ± 1.71 mm,4.31 ± 2.22 mm, 4.23 ± 1.94 mm, and 4.30 ± 1.57 mm at thebuccal side and 1.98 ± 0.88 mm, 2.79 ± 1.01 mm, 3.35 ± 1.27mm, and 3.93 ± 1.38 mm at the lingual side. The buccalcortical bone thickness in the maxilla was decreased fromGroup 1 to Group 3, while the thickness of palatal side wasno change. In the mandible, it did not show a tendency at thebuccal side and it was decreased from Group 1 to Group 3without significant difference at the lingual side. Therefore,the buccal side of the Group 1 and Group 2 in both themaxilla and mandible seems to be the most appropriate sitefor a mini-implant placement with taking the stability andretention.