Background: Oral squamous cell carcinoma (OSCC) is the most common malignant tumor of the oral cavity. The important cause of morbidity and mortality worldwide is due to its high tendency for metastasis. Moreover, mucoepidermoid carcinoma (MEC) comprises a significant proportion of oral tumors and are the most common neoplasms of the oral cavity after OSCC. The incidence of distant metastasis in salivary gland cancer is relatively low in comparison to OSCC.Nm23 is a metastatic suppressor gene that does not affect the growth of the primary tumor. This gene is identified by its decreased expression in metastatic tumor cells, compared to its expression in nonmetastatic cells. The overall increase in nm23 in the cytoplasm of cells might be important in the early development of OSCC, but increased amount of nuclear nm23 occurred in the metastatic state.The purpose of this study is to compare the metastatic potential of OSCC and MEC by immunohistochemical expression of nm23 protein.Material and Methods:Immunohistochemical staining with streptavidin peroxidase is used to analyze nm 23 expression in a total of 30 cases; 15 OSCC including well, moderately and poorly differentiated cases (7 metastatic and 8 non metastatic). Fifteen MEC cases including low, intermediate and high grade cases (8 metastatic and 7 non metastatic) were collected as archival paraffin embedded blocks.Results: Immunoreactivity for nm23 is nuclear in both OSCC and MEC with metastasis and cytoplasmic in non metastatic cases.Conclusion: Nuclear nm23 expression was seen in metastatic OSCC and MEC only, so nm23 could be considered as a metastatic marker and a marker of poor prognosis in both lesions.