It is well kwon that HPV have been strongly linked to progression of or al squamous cell carcinoma‘ Effici ent im mortalization of nonnal human oral keratinocyte(NHOK) should provid further evidence for the role HPV in tumorogenes is ‘ Because IHOK(I mmortali zed human oral keratinocyte) has been considered as a moclel syst em for study ing I-!PV- linkecl oral ca rcinogenes is , it is important to pursue the differenti ati al change of IHOK cul t ure moclel during t he culture passage, The purposes of this study were to examine the cha ra r’ ct eristic clifferential changes of cul turecl immorta lizecl human ora l keratinocytes during long term passage, and to apply these results to or al carcinogenes is in the future, NI-!OK was primarily incubated at 370C and 5% C02 under KBM bullet kJt IHOK was co ntinuously cul t ured towarcl 100th passage(two times per week) , Growth curve of NI-!OK and II-!OK clepend on clùture passage was taken For examining the cha racte ri s t ic clifferential changes of II-!OK, transrnission electron microscope, 1ì'ansgluta miase activity‘ E6/E7 mRNA detect ion, a ncl tumorogenecity were done 10th II-!OK showecl sl ight polygonal flattencl cells and sometimes apoptotic cells ‘ while 100th IHOK showecl increased polygonal cell s ‘ Cultu recl 100th IHOK showed r ela tively resis tant growth to high calcium than 10th II-!OK Microvilli from 10th II-!OK was not connect ecl with each other, ancl scatte red cytokeratin fil aments of 10th II-IOK. while decreased cytokeratin filaments in cytoplasm & prominent clesmosome of 100th IHOK. During the terminal differ entiation in cultured IHOK, induction of TGase 1 activity of 10th II-!OK was higher than that of100th IHOK mRNA E6E7 expresson was cletected and unchangable in both cul tured cells There was no tumorogenecity inclucecl by both culturecl cel ls. Although late passage IHOK showecl less r esemblance to NHOK, and lower TGase 1 acti vi ty than ea rly passage IHOK, it suggested that these cells should be 110t yet fully differ entiatecl to oral squ a mous ce ll carcinoma cells