Ki-67 antigen expression that reflected the proliferative activity of the tumor cells could be applied to fresh tissue and detection of the Ki-67 antigen in a stable formalin-fixed tissue using the MIB-1 monoclonal antibody was recently developed. The aim of this study was to observe whether or not Ki-67 antigen expression was correlated with the clinico-histopathological findings and DNA analyses. Authors performed immunohistochemical staining with the monoclonal antibody of Ki-67 and analysis of proliferation index and DNA contents in eighteen case of maxillary squamous cell carcinomas. The mucosa of chronic sinusitis was used as a control group. 1) Ki-67 positive nuclear area of maxillary squamous cell carcinomas(35.56±13.82%) was significantly higher than that of chronic sinusitis(11.65±3.17%)(p<0.05). 2) Both Ki-67 positive nuclear area and proliferation index were not to be significantly correlated(r=0.510, p=0.07). 3) The poor cellular differentiation showed higher Ki-67 positive nuclear area(p<0.05) and higher proliferation index(p>0.05). But Ki-67 positive nuclear area was not related with the clinical stages. As a result, Ki-67 antigen expression in maxillary squamous cell carcinomas could reflect the proliferative activity of tumor cells and was correlated with cell differentiation of tumor cells. The correlation to the clinical stages was not sufficient enough to be applied as a single prognosticator.