Ameloblastoma is a common odontogenic benign tumor of the jaw bone. However, it might be albe to infiltrate into the adjacent tissue, causing bony destruction and high recurrent rate. The aim of the study is to understand the biologic behavior of recurred ameloblastoma through immunohistochemical study. The PCNA, Ki-67, p53 and cytokeratin 17, cytokeratin 18 antibody staining were used. There was significant difference of positive reaction between non-recurred ameloblastoma and recurred ameloblastoma in PCNA and cytokeratin 17. There were no significant difference of positive reaction between non-recurred ameloblastoma and recurred ameloblastoma in p53, Ki-67 and cytokeratin 18. From the above results, it is suggested that the recurrence of ameloblastoma is related to positive reactions of PCNA and cytokeratin 17 and the progonsis of the recurrence of ameloblastoma is able to be predicted by using PCNA and cytokeratin 17.