Abstract: Objective: To evaluate the bone regeneration around the involved teeth in keratocystic odontogenic tumor (KCOT) after marsupialization. Methods: 12 cases with large mandibular KCOT were treated with enucleation and marsupialization. The area of KCOT, root length of involved teeth exposed to the cavity and thickness of peri-apical new bone were measured using panoramic and CBCT. The relationship between reduction of KCOT lesion's area and thickness of peri-apical new bone was evaluated by Pearson correlation analysis every three months. Results: 56 teeth were exposed to the cavity and average ratio of the root region covered by periodontal bone was 63.69% before marsupialization. In addition, 49 teeth were completely covered by new bone, and the roots of the other 7 involved teeth were partially covered by new bone with the ratio of 80.02%. The average ratio of root region covered by new bone was 97.5% in all the involved teeth. The average area of the cavity every 3 months was decreased by 2.23±0.94 cm², and the average thickness of peri-apical new bone every 3 months was increased by 1.57±0.72 mm. Meanwhile, the decreased area and increased thickness showed a significant correlation (r=0.908). Conclusion: Marsupialization could effectively promote the new bone formation to cover the peri-apical region of involved teeth.