e18562 Background: Although patients with locoregional advanced maxillary sinus squamous cell carcinoma (MSSCC) are often treated with surgery followed by postoperative radiotherapy (RT), the cosmetic and functional outcomes are unsatisfactory. Moreover, the efficacy and safety of intra-arterial chemoradiotherapy are controversial. Methods: In this study, we investigated the efficacy and safety of low-dose cisplatin administration through the superficial temporal artery (STA) combined with definitive RT in patients with MSSCC. Between January 2009 and December 2018, 57 patients were administered weekly intra-arterial infusions of cisplatin (30–50 mg/m2/5h) through the STA with simultaneous intravenous infusions of sodium thiosulfate. Overall response rate (ORR), local progression-free survival (LFS), maxillectomy-free survival (MFS), progression-free survival (PFS), overall survival (OS), and safety were evaluated retrospectively. The impact of clinical factors on survival was investigated using the Cox proportional hazard models. Results: The median follow-up time was 44 months (range, 10–80 months). There were 4, 26, 23, and 4 patients with cT2, cT3, cT4a, and cT4b, respectively. All patients completed the planned treatment except for one patient who discontinued owing to facial palsy. The ORR was 98% with 51 and 5 patients having complete and partial responses, respectively. The 3-year LFS, PFS, and OS were 74%, 63%, and 81%, respectively for all patients and 100%, 81%, and 94%, respectively for 22 patients received 70 Gy irradiation. Notably, the 3-year MFS was 95% for all patients and 100% in patients received 70 Gy RT. The most common grade 3 or more toxic event was oral mucositis (22.8%). Additionally, 4 (7.0%) patients had catheter-related infections. Late grade 3 or more adverse events included optic nerve disorder (8.8%), osteonecrosis (7.0%), encephalopathy (1.8%), and increased creatinine levels (1.8%). Salvage surgery including hard palate resection and orbital exenteration were performed in 2 and 1 patients, respectively. No clinical factor was correlated with survival outcomes in our study cohort. Conclusions: Low-dose cisplatin through STA combined with RT, especially 70 Gy RT, was associated with promising tumor response, high organ preservation rate, and tolerable adverse events in MSSCC patients. Further prospective studies are warranted to compare these outcomes with primary surgery.