Objective: To examine the expression patterns of p63 in tissues of particular keratinocyte original hyperproliferate diseases and variety cell types for determining if P63 is the marker of proliferative potential keratinocytes. Methods: P63 protein was detected and analyzed by immunoreactivity method and Western blot in biopsy specimens of keratinocyte original disorders including squamous cell carcinomas SCC, basal cell carcinomas BCC, Bowen’s disease and other tissues or cells, such as psoriasis vulgaris, normal skin tissues, primary cultured keratinocytes, immortal HaCaT cells, and epidermoid carcinoma cells A431. Results: P63 protein was expressed in the nuclei of basal and suprabasal layer of the epidermis, germinative cells of sebaceous glands in normal epidermal. P63 was strongly and diffusely detected in the majority of tumor cells in BCC and poorly-differentiated SCC. In Bowen’s disease, p63 expresses are remarkable in all cell layers. In the psoriasis plaque epidermal, p63 expressed mainly in basal cells and part of spinous cells. P63 expressed more strongly in primary cultured keratinocytes than in A431 cells or HaCaT cells. Conclusion: P63 is a nuclei marker of undifferentiated keratinocytes with the proliferative potential and may disrupt the terminal differentiation. The overexpression of p63 reflects immaturity of the tumor cells. The immunohistochemical staining of p63 may be useful for investigating the origin and differentiation of tumor cells.