Objective To investigate the relationship between mutations of KRAS and BRAF genes and distal colorectal adenoma and adenocarcinoma. Methods Lesion tissues of patients with distal colorectal adenoma (n=32, adenoma group) and adenocarcinoma (n=20, adenocarcinoma group) were obtained by endoscopic biopsy forceps. The genomic DNAs of lesion tissues were extracted and sequences of KRAS and BRAF genes were detected. Results Among 32 patients with adenoma, 7 of them were detected with KRAS mutations and the mutation rate was 21.9%. Among 20 patients with adenocarcinoma, 7 of them were detected with KRAS mutations and the mutation rate was 35.0%. Mutation types of codons 12 and 13 of KRAS gene of two groups were mainly G12D and G13D mutations. The difference of positive mutation rates of KRAS gene between two groups was not statistically significant (P>0.05). BRAF V600E mutation was not found in two groups. Conclusion Among Chinese patients with distal colorectal adenoma and adenocarcinoma, the mutation rate of BRAF V600E is low and that of KRAS gene is high. The difference of mutation rate of KRAS gene between distal colorectal adenoma and adenocarcinoma is not remarkable.