Mutation of p53 tumor suppressor gene is one of the most common genetic abnormalities in various human cancers. The wild-type p53 gene participates in suppressing cell transformation while the mutant-type p53 gene has oncogenic potential. The wild-type p53 protein that has a relatively very short half-life is found in normal cells with very low concentration and cannot be identified immunohistochemically. However, the mutant-type p53 protein that has a prolonged half-life accumulates in cells with high concentration and can be identified immunohistochemically. This study evaluated p53 expression by immunohistochemical staining with anti-p53 monoclonal antibody, Do-7(Novocastra Lap, Ltd), in 22 paraffin-embedded tissues of oral and laryngeal leukoplakia and investigated correlation between p53 expression and pathologic findings. Among 22 cases, five cases(22.7%) showed p53 positive expression. Pathologic findings of the p53 postive cases were 1 mild dysplasia(20%), 1 severe dysplasia(20%), 2 dyskeratosis(40%), and 1 hyperkeratosis(20%). Among 22 cases, only 1 case transformed to squamous cell carcinoma(4.5%).