The odontogenic keratocyst(OKC) is a common developmental odontogenic cyst and represents approximately 11% of odontogenic cysts. It is decided by microscopic and histopathologic determinant rather than by clinical appearance. In this study, expression of RANKL and OPG in OKC in relation to age and gender of patient and recurrence, location of lesion were examined through immuno- histochemical study. The RANKL and OPG antibody staining were used. The obtained result were as follow. 1. Positive immunoreactivity to RANKL/OPG in all specimens was found. 2. There was no significant difference in immunohistochemical expression of RANKL relating to recurrence, location of OKCs and age, gender of patients. 3. There was no significant difference in immunohistochemical expression of OPG relating to recurrence, location of OKCs and age, gender of patients. From above results, it is suggested that activation of osteoclasts by RANKL is an important mechanism by which OKCs cause bone destruction.