Ancient books from East Asia, especially, Korea, China and Japan, are all written in Chinese. Ancient mathematical books like 九章算術(Gujang Sansul in Korean sound, Jiuzhang Suanshu in Chinese) is not exceptional and also was written in Chinese. The book 九章算術音義(Gujang Sansul Eumeui in Korean, Jiuzhang Suanshu Yinyi in Chinese), a dictionary-like book on 九章算術was published by official 李籍(Lǐ Jí) of 唐(Tang) dynasty (AD 618-907). We discuss how to pronounce Chinese characters based on 九章算術音義. To do so, we compare the pronunciation of the characters used in the words which are explained in 九章算術音義, to those of the current Korean and Chinese. Surprisingly, the pronunciations of the Chinese characters are almost all accordant with those of both Korean and Chinese.