AIM: To investigate mutations of oncogene k-ras in colorectal cancer tissues and the relationship between mutations of k - ras and biological behavior of colorectal carcinoma. METHODS:The specimens of 123 patients with colorectal cancer were collected. Real - time fluorescence quantitative PCR were performed to detect k-ras mutations at codon 12 and codon 13 of exon 1, and the results were analyzed with the corresponding clinical pathological data. RESULTS: Among 123 colorectal cancer cases, point mutations were detected in 53 cases (40.8% ) , point mutations at codon 12 were found in 42 (34.1 % ) cases, and 11(8.9% ) cases at codon 13.No closely relationship between mutations of k-ras and tumor size, location, invasive depth and differentiation extent was observed. The rate of k-ras mutation in the cases with more invaded lymph nodes was higher than that in the cases without invaded lymph nodes ( P < 0.05 ) , and the rate of k-ras gene mutation in the cases with hepatic metastases was higher than that in no hepatic metastases (P <0.05). The rate of k - ras gene mutation was higher in TNM staging Ⅲ/Ⅳ than that in Ⅰ/Ⅱ( P < 0.05 ). CONCLUSION: Mutation of oncogene k-ras plays an important role in the carcinogenesis and development of colorectal cancer, and it is closely associated with invaded lymph notes and hepatic metastases, suggesting that mutation of k- ras indicates a poor prognosis.