Objective To study the protective effect of PCF against murine thymocytes apoptosis induced by UVB irradiation.Methods The irradiation damage model of thymocytes caused by UVB was established.Cellular ultrastructuralalterations were observed with TEM.The expressions of P53,Bax and Bcl-2 proteins were examined by immunocytochemical technique. The p38 mRNA gene expression was also determined with the technique of in situ hybridization.Results Apoptotic thymocytes were observed after UVB irradiation.The ultrastructural damages of the cells induced by UVB irradiation were reduced by the treatment of PCF.PCF also raised the expression of Bcl-2 gene and decreased the expression of P53,Bax.The mRNA expressions of p38 were decreased in PCF groups.Conclusion PCF showed significant protective effects on UVB-irradiated murine thymocytes in vitro.