Background: An unmet need for more effective and affordable kinase inhibitors remains in patients with progressive radioactive iodine-refractory differentiated thyroid cancer (RAIR-DTC) in China, where only sorafenib is approved for this indication. This study evaluated the 24-week objective response rate (ORR) to donafenib-a new, domestic multikinase inhibitor-in the treatment of locally advanced or metastatic RAIR-DTC in patients with measurable lesions. Two dose regimens (300 mg twice daily vs. 200 mg twice daily) were used to determine its optimal dosage and safety for further phase III studies. Methods: This study was a randomized, open-label, multicenter phase II trial. Thirty-five adult RAIR-DTC patients with at least one measurable targeted lesion according to RECIST 1.1 were enrolled from 12 centers in China and randomized to receive either 200 mg (17 patients) or 300 mg (18 patients) of donafenib orally twice daily for 24 weeks. The primary endpoint was ORR, and the secondary endpoints included progression-free survival (PFS) among others. Additionally, biochemical (serum thyroglobulin) and structural (total tumor diameter [TTD]) responses were assessed, change (ΔTTD) rates were calculated, and safety was evaluated. Results: The ORRs for the 200- and 300-mg arms were 12.5% and 13.33% (p = 1.000), respectively. The 300-mg arm had a nonsignificant, longer median PFS than the 200-mg arm (14.98 months vs. 9.44 months) (p = 0.351). There was a trend toward more tumor shrinkage in the 300-mg arm compared with the 200-mg arm (average ΔTTD rate -0.52 ± 0.71 vs. -0.04 ± 1.55 mm/month, p = 0.103). Most treatment-related adverse events (AEs) in both arms were grades 1-2. The most common grade 3 treatment-related AEs in both arms were palmar-plantar erythrodysesthesia and hypertension; the sum occurrence rates of these two AEs in the 200-mg and 300-mg arms were 11.43% and 22.86%, respectively. Conclusions: Donafenib was generally well tolerated. Both donafenib regimens demonstrated similar efficacy in terms of the ORR in locally advanced or metastatic RAIR-DTC. The results warrant further studies on donafenib as a new, feasible treatment option for RAIR-DTC patients. Clinical Trials.gov IDs: NCT02870569; CTR20160220.