Combination therapy with S-1, superselective intra-arterial infusion of CBDCA and radiation therapy has been used to treat patients with oral cancer since 2005. In this study, the histopathological effects and toxicities following concurrent chemoradiotherapy were examined. The subjects consisted of 15 patients (10 men and 5 women) who were treated with S-1 (60-80 mg/day, 4 weeks), superselective intra-arterial infusion of CBDCA (300 mg/body) and radiation therapy (total dose 30-36 Gy) in our department from 2005 to 2009. Nine patients, showed T2 disease, 3 showed T3 disease, and another 3 showed T4 diseases. The primary cancer sites were the tongue (6 cases), buccal mucosa (4 cases), mandible gingival (3 cases), maxillary gingiva (1 case), and the floor of the mouth (1 case). The histopathological effects were evaluated according to Oboshi-Shimosato classification. Grade IV was shown in 10 cases (66. 7%), grade III in 1 case (6. 7%), II bin 3 cases (20. 0%), and II a in 1 case (6. 7%). All patients completed the treatment. The pathological response of the resected tumor was grade IIbor higher in 14 cases (93. 3%). While good histological effects were noted, there was one patient for whom viable tumor cells remained in the central part of the tumor. The present study indicates that further investigation is needed to determine the best dosing and dosing schedule.