A dose-finding and efficacy confirmation trial was started in Japan in April 2014 to evaluate the efficacy and safety of superselective intra-arterial infusion of cisplatin and concomitant radiotherapy for locally advanced maxillary sinus cancer. A total of 18 patients will be enrolled in the dose-finding phase for the determination of the recommended number of cisplatin cycles, and 65 patients with T4aN0M0 and 62 patients with T4bN0M0, including those who received the recommended number of or fewer cycles in the dose-finding phase, will be enrolled from 16 institutions within a 5-year period in the efficacy confirmation phase. The primary endpoints of the dose-finding and the efficacy confirmation phases are dose-limiting toxicities and 3-year overall survival, respectively. This trial was registered at the UMIN Clinical Trials Registry (http://www.umin.ac.jp/ctr/) under Trial No. UMIN000013706.