Abstract: 【Abstract】 Objective To investigate the incidence of P53 and K-ras gene mutation in colorectal adenomas and primary colorectal carcinomas. Methods There were 25 normal samples, 38 samples of colorectal adenoma, 78 samples of single primary colorectal cancer and 19 samples of multiple primary colorectal carcinomas (7 synchronous colorectal carcinomas and 12 metachronous colorectal carcinomas) collected in this study. With the analysis of clinico-pathologic features for each patient, exon 5-8 of P53 gene and codon 12-13 of K-ras gene of each sample were extended by real-time PCR. Multi-factor correlation analysis was carried out between the clinicopathologic features and the mutation of P53 and K-ras gene in colorectal adenoma and primary colorectal cancer. Results The P53 gene mutation is 0% (0/25)，44.8%（17/38），43.6%（34/78）and 42.1%（8/19）respectively in normal mucosa tissue, colorectal adenomas, single lesion and multiple lesion of primary colorectal carcinomas, while the proportion of K-ras gene mutation was 0%（0/25），18.4%（7/38），39.7%（31/78），47.4%（9/19）respectively. In our investigation there were obvious statistical differences as to the proportion of mutation of the P53 and K-ras gene between normal mucosa tissue and other three groups respectively (P<0.05）, while statistical differences as to the proportion of mutation of K-ras gene were found between colorectal adenomas group and single or multiple colorectal carcinoma group (P<0.05）. There was significant statistical difference between P53 and K-ras gene mutation in colorectal adenomas (P<0.05）. In addition, there were no statistical differences as to the proportion of mutation of the P53 and K-ras gene between the stageⅠ,Ⅱand well-differentiated ones of primary colorectal cancers and the stageⅢ Ⅳ and poorly-differentiated ones. There was no relationship between the age, gender, family history and tumor locations of the patients and the mutation of the P53 and K-ras gene. The stage and grade of differentiation of cancer was not the risky factor of the mutation of the P53 and K-ras gene in primary colorectal cancers. Conclusion The cancers. Conclusion results of this study not only suggest that mutation of P53 suppressor gene and K ras play a significant role in the procedure of colorectal tumorigenesis, but also indicate that the mutati on of P53 gene occurs earlier than K-ras mutation does during tumorigenesis.