Abstract: The amplification and the G-T mutation at codon 12 of the C-Ha-ras oncogene in oral leukoplakia tissues were analyzed by using polymeras chain reaction (PCR) and molecularbiologic technique.The results showed that these tissues have no amplification of Ha-ras oncogene, Only one case harbored G-T mutation in 11 oral leukoplakias, but this mutation was absent in 10 normal oral mucosal tissues. The possible role and signlficance of C-Ha-ras oncogene in oral premalignant lesions had also been discussed.