Development of oral mucositis represents a rate-limiting factor in radiation therapy for the treatment of head and neck, as well as other cancers. In this work, we investigated the treatment effect of ecdysterone (a steroid derived from the dry root of Achyranthes bidentate) on radiation-induced oral mucositis, and examined possible underlying mechanisms. Male Sprague-Dawley rats were exposed to 20 Gy X-ray irradiation (single dose, cranial localization) to induce oral mucositis. Possible therapeutic effects of ecdysterone on radiation-induced oral mucositis were investigated by monitoring weights, direct observations, visual scoring method and evaluation of hematoxylin and eosin staining. Assessments of leukocyte common antigen and proliferating cell nuclear antigen staining were also performed in the damaged areas of tongues harvested after irradiation, and changes in signaling pathways were investigated using Western blotting. The development and progression of radiation-induced oral mucositis in this model was similar to that observed in clinic patients. Ecdysterone effectively improved radiation-induced oral mucositis as assessed by direct observation and histopathology, and also increased proliferation of matrix cells, since the Ras-Raf-ERK signal pathway was found to be activated by its use. It was concluded that orally administered ecdysterone accelerated the healing process in a rat model of radiation-induced oral mucositis by upregulating the Ras-Raf-ERK signal pathway.