Abstract: Objective: The aim of this study was to evaluate the relationship between k-RAS gene mutation and the resistance to epidermal growth factor receptor-tyrosine kinase inhibitor (EGFR-TKI) treatment in patients with nonsmall-cell lung cancer (NSCLC). Methods: Forty-five pathologies confirmed NSCLC patients who received EGFR-TKI (Gefitinib) treatment were retrospectively included in this study. The mutation of codon 12 and 13, located in exon1 and exon 2 of k-RAS gene were examined by polymerase chain reaction (PCR) and DAN sequencing in tumor samples of the included 45 NSCLC patients. The correlation between Gefitinib treatment response and k-RAS mutation status was analyzed in tumor samples of the 45 NSCLC patients. Results: Eight tumor samples of the 45 NSCLC patients were found to be mutated in coden 12 or 13, with an mutation rate of 17.8% (8/45); the objective response rate (ORR) was 29.7%(11/37) with 1 cases of complete response (CR) and 10 cases of partial response in k-RAS mutation negative patients. Furthermore, the ORR was 0.0% in k-RAS mutation positive patients with none CR. The ORR between k-RAS mutation and nonmutation patients were significant different (P Conclusion: k-RAS gene mutation status was associated with the response of Gefitinib treatment in patients with NSCLC.