The eukaryotic translation initiation factor 5A (eIF5A) is a ubiquitous protein of eukaryotic and archaeal organisms which undergoes hypusination, and known to play pivotal functions for the synthesis of proteins involved in cell proliferation and cell cycle control. Its nuclear localization has an important implication for the eIF5A functions in nucleus, but the evidence of the nuclear translocation is still in controversy. This study is aimed to elucidate the nuclear localization of eIF5A in the epithelial cells of oral leukoplakia by the immunohistochemistry using trypsin digestion to remove their cytoplasms. The keratinocytes of the acanthotic and basal cell layers in oral leukoplakia showed the complete removal of their cytoplasmic components, but the nuclei of those cell layers were remained on the microsection. The immunostainings using both polyclonal and monoclonal antibody against eIF5A showed the strong positive reaction in the nuclei remained after trypsin digestion. And the immunostaining was more intensely expressed in the nuclei of the basal and suprabasal keratinocytes than in the nuclei of the upper spinous keratinocytes. These data directly indicate the post-translationally modified eIF5A is abundantly localized in the nuclear matrix components including nucleoli, which are resistant to the trypsin digestion. It is also presumed that the nuclear eIF5A localized at the trypsin resistant nuclear matrix, i.e., histone and r ibosomal proteins, may be closely relevant to the control of mRNA production or to the nuclear-cytoplamic trafficking for mRNA transportation.