Abstract: IRESSA (ZD1839, Gefitinib), an orally selective drug inhibitor of the epidermal growth factor receptor (EGFR) tyrosine kinase (TK), have been approved in the management of patients with advanced, chemotherapy-refractory non-small cell lung cancer (NSCLC) in several countries. Recently, how to predict the reponse to IRESSA has become a focus on enhancing the clinical effect of IRESSA to NSCLC patients. In this review, we discussed recent progression in three aspects, including patients' characteristics and efficacy of IRESSA, the expression of EGFR or its downstream molecules and IRESSA efficacy, and the mutational status of EGFR and IRESSA efficacy.