Epidermal growth factor receptor tyrosine-kinase inhibitors (EGFR-TKIs) are standard treatment for advanced non-small cell lung cancer (NSCLC) patients with epidermal growth factor receptor (EGFR) mutation. However, EGFR mutation testing is not attainable in approximately 20% of patients. The current study examined intercalating and maintaining gefitinib treatment in stage IIIB/IV non-squamous NSCLC, never or former light smoking patients with unknown EGFR mutation status. Briefly, 219 patients who achieved stable disease (SD) with gemcitabine (1250 mg/m2) plus carboplatin (5 AUC) were randomized at 1:1 ratio to continue chemotherapy (n = 110) or intercalating gefitinib (250 mg/day on days 15-25 of each cycle until disease progress (n = 109). Progression-free survival (PFS) was 9.7 vs. 4.2 month in the gefitinib vs. control arm (HR: 0.41, 95% CI: 0.31-0.56; P < 0.001). Overall survival (OS) was also longer in the gefitinib arm (20.1 vs. 15.4 months; HR: 0.68; 95% CI 0.48-0.97; P = 0.0323). Adverse events, including diarrhea, dermal reaction and thrombocytopenia, were more common in the gefitinib arm. In conclusion, intercalating and maintenance gefitinib treatment is a viable option for advanced NSCLC patients with unknown EGFR mutation status in subpopulations with high EFGR mutation rate.