Chromosomal abnormality s uch as aneuploidy is one of the main factors to cause cancers This abnormality is caused by defects in centrosomal duplication‘ and most cancer cells have extra copies of centrosomes, r esulting in t he formation of multipolar spindles. Several kinases playing in mitotic phase have been implicated in regulating the centrosomal cycle‘ spindle checkpoint‘ and chromosome co ndensation and segregation. They also have Lhe ability to act as oncogenes. FOl studying the relationship between rnitotic kinase and oral cancers, the kinase activity of polo-like kinase-1, which is one of mitosis-specific kinases, is analyzed in oral carcinoma cells originated differently. Kinase activity was increased in these cancer cells compared to normal human gingival fibroblast primary cultured cells Moreover. the mitotic cell populations were a lso increased in these cell lines. Whereas the inhibition of Polo-like kinase-1 by C-terrninal domain in human gingival fibroblast cells induced multiploidy‘ the apoptotic cell population was increased in oral cancer cells overexpressed C-terminal domain 0 1' Polo- Ii ke kinase-1. These data suggested that polo-like kinase-1 might be involved in the on cogenic effect in oral cancer like other solid human carcinomas, and be target molecules for anti-cancer drug.