We report two cases of idiopathic orbital myositis treated with radiation therapy (RT). Both patients visited our hospital with complaints of orbital pain on eye movement and eyelid swelling. There was no history of thyroid disease or trauma, and no signs of infection, neoplasm, or collagen disease. The laboratory investigations, including a thyroid function test, showed no abnormalities in either woman. They were initially treated with a combination of corticosteroids (CS) and nonsteroidal anti-inflammatory drugs (NSAIDs), however, they became dependent on or refractory to oral CS therapy, and received 20 Gy in 10 fractions of RT to the orbit. Their symptoms decreased immediately, and both patients were able to reduce the dosage of oral CS after RT. One patient could completely withdraw oral CS thereafter. However, they both experienced recurrence at eight months after RT, and have been receiving oral CS to control their symptoms. RT at doses of 20 Gy in 10 fractions for patients with idiopathic orbital myositis appears to be effective in palliating symptoms, but long-term control is not satisfactory.