Oral squamous cell carcinoma (OSCC) is now the forth leading cause of male cancer mortality in Taiwan. The betel quid (BQ) chewing is the main cause OSCC in Taiwan. This study was aimed to clone the CDK2-associated protein 1 (CDK2AP1) complete CDs and characterization of its expression profiles as well as protein sublocalization in oral cancers. The human CDK2AP1 gene is 1.6 Kbp in length, mapped to 12q24.31 and encodes for a 12.4 kDa polypeptide. Human CDK2AP1 protein interacts with DNA polymerase alpha/primase resulting in negative regulation of the rate of initiation of DNA replication. It has been reported that differential CDK2AP1 expression, with decreased or absent expression in microsatellite-unstable (MSI+) colorectal cancer (CRC) cell lines, suggesting that loss of CDK2AP1 protein expression is a characteristic of malignant transformation in MSI+CRC. The role of CDK2AP1 in the onset or progression of oral cancer is still unknown. In this study, we firstly extracted RNA from 45 patients¡¦ specimens. Then, we cloned CDK2AP1 CDs from stomach carcinoma cell line (Scm1) and subcloned into various protein expression vectors for further examining CDK2AP1 subcellular localization in HeLa cell. Polyclonal CDK2AP1 antibody was prepared. We have demonstrated that the CDK2AP1 protein locates in both cytoplasm and nucleus by immunofluorescence analysis. In addition, we examined the CDK2AP1 mRNA expression profiles in oral cancer specimens by quantitative RT-PCR. The results showed that the expression of CDK2AP1 mRNA in oral cancer tissues were higher than those in normal oral tissues. Furthermore, we have determined and compared the CDK2AP1 protein in both oral cancer and normal tissues by immunoblotting analysis and immunohistochemical (IHC) analysis. The results from both immunoblotting and IHC were consistent with the results from quantitative RT-PCR. CDK2AP1 protein expression was higher in oral cancer tissues than in normal oral tissues.