To study the expression of matrix metalloproteinase(MMP) and tissue inhibitor of metalloproteinase (TIMP) in ameloblastoma (AB) and to determine the relationship between biological behavior of AB and clinical pathology.The specimens of 43 cases of AB, 10 cases of odontogenic keratocyst (OKC), 8 cases of normal oral mucosa were examined by streptavidin-biotin method.In 8 cases of normal oral epithelial, MMP-2 was negative or weak positive. In OKC, MMP-2 was extensively positive in stratum spinosum of 2 cases, and weekly or negative in stratum basale. MMP-2 was strongly expressed in the central and peripheral cells of the tumor islands in 28 cases of AB. There were difference among these three groups (P < 0.001). Comparing AB with normal oral mucosa and OKC, there was significant difference (P < 0.05). MMP was positive expressed in cells of stroma. The positively rate and intensity increased as AB recurrence and transformed malignantly, but were not associated with age, sex, pathological type and location. TIMP-1 was weakly or not expressed in normal oral mucosa, stoma, OKC and AB.The high expression of MMP-2 and MMP-9 is related to the biological behavior of AB. Imbalances of the expression of MMP-2 and MMP-9 protein maybe be one of the facts of the invasion of AB. The MMPs activation produced by stromal cells may be also be related to the invasion of AB.