Somatic mutation in the tyrosine kinase (TK) domain of the epidermal growth factor receptor (EGFR) gene is associated with the sensitivity of non-smal cell lung cancer (NSCLC) to TK inhibitor Gefitinib. Mutational analysis for EGFR exons 19 and 21 was performed in 75 NSCLC and 10 breast cancer patients. All patients had not received treatment of Gefitinib. Somatic mutations in TK domain of EGFR were identified in 13 of the 75(13/75, 17.33%) patients, including 7 cases of in-frame deletion in exon 19 (7/75, 9.33%) and 6 cases of amino acid substitution (2573T>G, L858R) in exon 21 (6/75, 8%) . No other mutations were found in 10 breast cancer patients who stained positive for HER2 immunhistochemistry. Adenocarcinoma has a higher rate of mutations than several other types of NSCLC, the mutations occurring more fre-quently in female patients. EGFR mutation rate in Chinese NSCLC patients was higher than that in Caucasians. Our data indicated that Chinese adenocarcinoma patients could benefit from TK inhibitor Gefitinib.