Abstract: Objective To study the correlation between K-ras mutation and prognosis of patients with stageⅢ colorectal cancer（CRC） receiving postoperative adjuvant chemotherapy. Methods Forty patients with stageⅢ CRC who underwent operation and postoperative adjuvant chemotherapy from January 2005 to December 2010 in our hospital were enrolled in this study.Their K-ras mutation on codons 12 and 13 was detected by PCR and DNA sequencing.Correlation between clinicopathologic and molecular characteristics and survival time was analyzed. Results The K-ras mutation rate was 15%（6/40）.The gender and age of patients,site,pathological grade and type,T and N staging of the disease were not related with the K-ras mutation.Thirty-four patients（85%） had recurrence or metastasis and 9 patients（22.5%） died from January 2005 to December 2010.The median overall survival（OS） time was 48.460 months,the median disease-free survival（DFS） time was 11.992 months,the 1-,3-,and 5-year survival rate was 97%,73% and 51%,respectively.Univariate analysis showed that the DFS time of patients with wild-type K-ras was longer than that of those with mutant K-ras（P＜0.001）.The other pathological parameters had no effect on the DFS time.However,the age of patients,pathological grade and recurrence or metastasis within 1 year were the factors influencing the OS,while the other pathological parameters and K-ras mutation had no effect on the OS.Cox multivariate analysis showed that the K-ras status was an independent risk factor for the DFS time,while the age of patients and recurrence or metastasis of the disease within 1 year（P=0.006） were the independent risk factors for the OS. Conclusion The DFS time of colorectal cancer patients with wild-type K-ras receiving postoperative adjuvant chemotherapy is longer than that of those with mutant K-ras,indicating that the K-ras gene can be used as an indication for the therapeutic effect of adjuvant chemotherapy on postoperative colorectal cancer.