Five cases of ameloblastoma considered to be originated from the wall of the odontogenic cysts are reported. Histologic characteristics and diagnostic criteria are aimed to study in differentiation of ameloblastoma arising in odontogenic cysts from odontogenic cysts accompanying with reactive epithelial proliferation, and the literature is reviewed. This study can propose that the ameloblastic change and downward growth of epithelial cells lining the cysts are the most important and characteristic findings of the ameloblastoma derived from odontogenic cysts. In addition, the intraluminal proliferation of epithelial cells in plexiform pattern is also significant.