Odontogenic cysts are classified into inflammatory and developmental origins. The most common representative inflammatory cyst is periapical cyst and the most common representative developmental cyst is dentigerous cyst and cyst which show character of tumor is odontogenic keratocyst and cyst of which cystic epithelial lining cells transform to ameloblastoma is unicystic ameloblastoma. Proliferation studies are needed because of various causes, different clinical and pathologic findings. Recently Ki67 has been generally used as cellular proliferation marker, which is closely related to proliferation. Because Ki67 exists in all the time of cell mitosis stage including G1, S, G2, and M, but disappear in resting phase, G0, it is widely used in the evaluation of cell and tissue proliferation activity. The purpose of this study was to establish clinical therapeutic standard through clinical prognosis associated with Ki67 protein expression because of various causes, different clinical and pathologic findings. Immunohistochemical study was performed in selected each 10 biopsy cases through LSAB reaction and HRP system using anti-Ki67 monoclonal antibody. Ki67 expression was mainly seen in the basal layer of periapical cyst, dentigerous cyst and unicystic ameloblastoma, and in suprabasal layer of odontogenic keratocyat, while positive cells appeared very low frequently in unicystic ameloblastoma. Ki67 expression was mainly observed around inflammatory area. Ki67 expression appeared to be independent on the destruction and recurrence of cystic lesion. Conclusively, high cellular proliferation could not represent destruction and recurrence degree of lesion, but this proliferation might be closely associated with circumstance such as inflammation