Lenvatinib has shown efficacy in treating radioiodine-refractory differentiated thyroid cancer (RR-DTC) in the multinational phase III SELECT study; however, it has not been tested in Chinese patients with RR-DTC.Chinese patients with confirmed RR-DTC (n = 151) were randomly assigned 2:1 to receive lenvatinib 24 mg/day or placebo in 28-day cycles. The primary endpoint was progression-free survival, and key secondary endpoints included objective response rate and safety. Analyses for progression-free survival and objective response rate were conducted using Response Evaluation Criteria in Solid Tumors v1.1 and confirmed by independent imaging review. All adverse events were assessed and monitored.Progression-free survival was significantly longer with lenvatinib treatment [n = 103; median 23.9 months; 95% confidence interval (CI), 12.9-not estimable] versus placebo (n = 48; median 3.7 months; 95% CI, 1.9-5.6; hazard ratio = 0.16; 95% CI, 0.10-0.26; P < 0.0001). The objective response rate was 69.9% (95% CI, 61.0-78.8) in the lenvatinib arm and 0% (95% CI, 0-0) in the placebo arm. At data cutoff, 60.2% of patients receiving lenvatinib remained on treatment; treatment-emergent adverse events led to lenvatinib discontinuation in 8.7% of patients. Overall, treatment-emergent adverse events of grade ≥3 occurred in 87.4% of patients in the lenvatinib arm, the most common being hypertension (62.1%) and proteinuria (23.3%).Lenvatinib at a starting dose of 24 mg/day significantly improved progression-free survival and objective response rate in Chinese patients with RR-DTC versus placebo. There were no new or unexpected toxicities. Results are consistent with those from SELECT involving patients with RR-DTC.©2021 The Authors; Published by the American Association for Cancer Research.