© 2017 Wiley Periodicals, Inc. Background: We are currently undertaking a multi-institutional prospective trial of the superselective intra-arterial infusion of high-dose cisplatin with concomitant radiotherapy for patients with T4aN0M0 or T4bN0M0 locally advanced maxillary sinus squamous cell carcinomas (SCC). We herein report the results of the dose-finding phase. Methods: The dose-finding phase sought to evaluate the incidence of dose-limiting toxicities and determine the recommended number of cycles of the intra-arterial infusion of cisplatin. In this phase, 100 mg/m2 of cisplatin was administered intra-arterially weekly for 7 weeks with concomitant radiotherapy (70 Gy). Results: All 18 patients received a full dose of radiotherapy. The number of cycles of cisplatin was 7 in 13 patients and 6 in 5 patients. The dose-limiting toxicities were observed in 5 patients. Conclusion: These results indicated that this therapy is safe and well-tolerated at 7 cycles of cisplatin, which was determined to be the recommended number of cycles for locally advanced maxillary sinus SCC.