This paper focused on examining the system and contents of Saseong Tonghae (四聲通解, a Chinese rime dictionary compiled by Choi Se-jin) and understanding its value. As a result, it was found that Saseong Tonghae is based on HongmuJeong-un(洪武正韻), but shows Korean originality in rime classification system and initials arrangement. In particular, it is noticeable that the initials arrangement corresponds to the sequence of initial phonemes arrangement in Hunminjeong-eum Haeryebon(訓民正音解例本, a book explaining the principles of Hangul), which is the outcome of research on Chinese phonology during the Joseon Dynasty in the 15th century. Besides, based on the fact that pronunciations revised or newly suggested in Saseong Tonghae are reflected in (Beonyeok) Nogeoldae((飜譯)老乞大, The first translation of Nogeoldae, a foreign language textbook from the Joseon Dynasty), (Beonyeok)Bak Tongsa((飜譯)朴通事, The first translation of Baktongsa, a foreign language textbook from the Joseon Dynasty), and (No-Bak)Jipram((老朴)輯覽, Choi Se-jin’s explanation of difficult-to-understand words in Nogeoldae and Baktongsa), this paper argues that the relevant books were published together. And this paper confirms that after its publication, Saseong Tonghae had a tremendous effect on the history of research on Chinese phonology during the period of Joseon Dynasty, since even Gyujang-Jeonun(奎章全韻), the last Chinese rime dictionary in the Joseon Dynasty, was based on the pronunciations of Saseong Tonghae.