An immunohistochemical method utilizing avidin-biontin complex (ABC) technique was used in this study to detect P16 and P53 protein expressions in 40 ovarian serous cystadenocarcinomas and 10 serous cystadenomas. The results showed that the total positive rates of P16 and P53 protein were 40% and 60% respectively. The positive staining rate was higher in P53 protein expression than in P16 protein expression in the same cases. The positive staining rates of P16 protein were 16.67%, 33.33% and 52.63% respectively in stages I, II and III. There was no significant difference in histological grading. The postive staining rate of P53 protein expression in poorly differentiated tumor was higher than that in well differentiated group (P < 0.05). These results suggested that P16 and P53 protein expressions of the ovarian serous cystadenocarcinoma might be correlated with human organs, histological type of tumor, cyclin and cyclindependent kinase.