Background: Combination of tyrosine kinase inhibitor (TKI) and chemotherapy has shown improved clinical outcomes in advanced epidermal growth factor receptor (EGFR) mutated non-small cell lung cancer (NSCLC) patients. We conducted this phase 3, randomized, controlled trial to further investigate the clinical efficacy and safety of gefitinib combined with chemotherapy in EGFR mutated NSCLC patients with brain metastases. Methods: Treatment-naïve, confirmed brain metastases and EGFR sensitive mutated NSCLC patients were screened from six centers in China. The eligible patients were randomly assigned (1:1) to receive gefitinib alone or gefitinib plus pemetrexed-platinum chemotherapy until intracranial progressive diseases, unacceptable adverse, or any cause of death. Theprimary endpoint was intracranial progression-free survival (iPFS), secondary endpoints were PFS, overall survival, intracranial objective response rate, overall objective response rate, and safety. This study is registered at ClinicalTrials. gov, number NCT01951469. Results: From January 2017 to June 2021, 161 patients were randomly assigned to receive gefitinib (n = 81) or gefitinib plus pemetrexed-platinum chemotherapy (n = 80), the median follow-up time was 18.2 (IQR 11.8-29.7) months. The median intracranial PFS was 15.6 (14.3-16.9) months in gefitinib plus chemotherapy group versus 9.1 (8.0-10.2) months in gefitinib group (HR = 0.36, 95% CI, 0.25-0.53, P < 0.001). Similarly, the median PFS was also significantly longer in gefitinib plus chemotherapy than gefitinib alone (16.3 months vs 9.5 months, P < 0.001). In addition, gefitinib plus chemotherapy had better intracranial objective response rate (85.0% versus 63.0%, P = 0.002) and overall objective response rate (80.0% versus 64.2%, P = 0.035) than gefitinib alone. At the data cutoff, 50.3% of patients (35 patients in gefitinib plus chemotherapy group and 46 patients in gefitinib group) had died. The 3-year OS rate was significantly higher in gefitinib plus chemotherapy group (47.4%, 95% CI 36.3-58.7) than in gefitinib group (24.9%, 95% CI 15.1-34.3, P = 0.003). And median overall survival was 35.0 months (95% CI, 28.8-41.3 months) in gefitinib plus chemotherapy group versus 28.9 months (95% CI, 23.4-34.4 months) in gefitinib group (HR = 0.66, 95% CI, 0.42-1.03, P = 0.065). Grade 3 or worse adverse events were more common in gefitinib plus chemotherapy group (40.0% versus 21.0%, P = 0.010), but most of them were manageable. Conclusions: Inuntreated EGFR mutated NSCLC patients with brain metastases, gefitinib plus chemotherapy significantly improved intracranial PFS, PFS and a tendency of OS than gefitinib alone, and could be the optional first-line treatment. Clinical trial information: NCT01951469.