OBJECTIVE To investigate gene mutations of epidermal growth factor receptor (EGFR) and K-RAS (Kirsten rat sarcoma viral oncogene) in Chinese patients with non-small cell lung cancer (NSCLC), and study the correlation with its protein expression and its clinical significance on gefitinib. METHODS Detect the EGFR and K-RAS gene mutations status by gene sequencing and use the method of Immunohistochemistry to detect EGFR and K-RAS protein expression. RESULTS The frequency of EGFR mutations was 33%, mainly located in exon 19 and exon 21. The frequency of K-RAS mutations was 5.5%, mainly located in codon 12. There was no case which both had EGFR and K-RAS mutations, suggesting a mutually exclusive relationship between the two. EGFR mutations are more common in adenocarcinomas (particularly those with bronchioloalveolar features), nonsmokers and females. 16% were detected EGFR positive expression and had no correlation with EGFR mutation (P > 0.05), but had significant correlation with mutation in exon 19 (P < 0.05). The frequency of K-RAS positive expression was 52.5% and had no correlation with K-RAS mutation (P > 0.05). Twelve (8 cases were protein-negative) out of 15 gefitinib-treated NSCLC patients with disease control carry EGFR mutations. CONCLUSION EGFR protein expression has some correlation with exon 19 mutations. Combined detection of EGFR and K-RAS gene mutations can help clinicians to choose patients who may benefit from EGFR tyrosine kinase inhibitor (EGFR-TKI) and to predict the response and prognosis of gefitinib.