Radiotherapy is classified into external beam radiotherapy and brachytherapy. Recently, advancement of precision radiotherapy including stereotactic radiotherapy and intensity-modulated radiotherapy （IMRT） has brought remarkable clinical outcomes and high treatment quality. Indeed, chemoradiotherapy for pharyngeal cancer is now considered as definitive treatment by overcoming the parotid gland damage using IMRT. On the other hand, most of oral cancer patients are still treated by surgery. Two main reasons could be the anatomical position of oral cancer surrounded by maxilla and mandible, and cellular radioresistance of oral cancer cells compared to pharyngeal cancer cells. In this situation, only brachytherapy, giving radiation from inside of tumor tissues by implanting sealed radioisotopes, has been applied as definitive radiotherapy for early stage oral cancer with good clinical results. Two types of brachytherapy exist in terms of dose rate, high and low. In this review, the status quo and biological superiority of low-dose rate brachytherapy will be described.