The aim of this study was to evaluate the efficacy and safety of antiulcer oral mucosal protectant-RADoralex® in the prevention and treatment of radiation-induced oral mucosal reactions elicited during intensity-modulated radiation therapy (IMRT). for locally advanced nasopharyngeal carcinoma (NPC). A total of 90 patients with locally advanced NPC who developed post-treatment grade 1 oral mucositis were selected for this study. They were randomly assigned to the experimental group (n = 44) treated by mouth rinsing with the RADoralex® during radiochemotherapy and the control group (n = 43) treated by mouth rinsing with sodium bicarbonate solution, and the patients' oral mucosal conditions, quality of life, weight change and oral pain levels were analyzed. The incidence of Common Terminology Criteria for Adverse Events (CTCAE) v4.0 grade 2 and grade 3 oral mucositis were significantly lower in the experimental group than in the control group. Compared to the control group, the time to progression, and the time from the end of treatment to oral mucosa healing in the experimental group was significantly shorter. The experimental group lost 8.66 ± 3.543% of their body weight during treatment period, while the control group lost 12.53 ± 4.284% (p < .001). From the beginning the 3rd week of treatment to the 2nd week after the end of treatment, the Oral Mucositis Assessment Scale (OMAS) scores were lower in the experimental group than in the control group (p < .05). RADoralex® significantly reduced the incidence and severity of oral mucositis in patients with locally advanced NPC during radiochemotherapy, delayed the progression of oral mucositis.