Polymorphous low-grade adenocarcinoma is a rare malignant tumor that mainly occurs in salivary glands, particularly in the hard palate. To date, surgery has been the most commonly used treatment method with the aim of achieving negative margins of resection. Here, we report a case of a 51-year-old woman who presented with a painless growing mass in her oral cavity with Rouviere's lymph node metastasis. Laboratory data showed severe anemia because of bleeding from the tumor. We inserted two catheters into the bilateral external carotid arteries via the superficial temporal arteries, and began continuous intra-arterial infusion with cisplatin and a cisplatin-neutralizing agent. The bleeding stopped after the first infusion, and we continued with weekly arterial cisplatin infusion and proton beam therapy (70.4 GyE in 32 fractions). A decrease in tumor volume has been maintained for 2 years, with no evidence of new metastasis.