Carboxyamidotriazole (CAI), a calcium channel blocker, inhibits tumor cell proliferation, metastasis, and angiogenesis. This trial aimed to determine whether CAI combined with conventional chemotherapy could prolong progression-free survival (PFS) in non-small cell lung cancer (NSCLC) patients. Patients were assigned into groups (3:1 ratio) to receive either chemotherapy + CAI or chemotherapy alone. Cisplatin (25 mg/m2) was administered by intravenous infusion on days 1, 2, and 3, and vinorelbine (25 mg/m2) on days 1 and 8 of each 3-week cycle for four cycles. CAI was administered at 100 mg daily with concomitant chemotherapy; this treatment was continued after chemotherapy was ceased until serious toxicity or disease progression had occurred. PFS was the primary endpoint, and the secondary endpoints were objective response rate (ORR), disease control rate, overall survival (OS), and quality of life. In total, 495 patients were enrolled in the trial: 378 in the chemotherapy + CAI group and 117 in the chemotherapy + placebo group. PFS was significantly greater in the chemotherapy + CAI [median, 134 days; 95% confidence interval (CI) 127-139] than in the chemotherapy + placebo (median, 98 days; 95% CI: 88-125) group, with a hazard ratio of 0.690 (95% CI: 0.539-0.883; p = 0.003). There was no difference in the OS rates of both groups. The ORR was greater in the chemotherapy + CAI group than in the chemotherapy + placebo group (34.6% versus 25.0%, p = 0.042). Adverse events of ⩾grade 3 occurred more frequently in the CAI group [256 (68.1%) versus 64 (55.2%); p = 0.014]. CAI + platinum-based chemotherapy prolonged PFS and could be a useful therapeutic option to treat NSCLC. chinadrugtrials.org.cn identifier: CTR20160395. © The Author(s), 2020.