There are no documents in Korea to show how the Chinese characters we use today were pronounced until 15th century. 1. Ancient Japanese documents, however, provide ample material which shows how names of people, places, and government posts were pronounced in the three Kingdoms period. According to Nihonshogi, it was Koreans who taught Chinese to Japanese and were responsible for recording and making these Japanese documents. 2. According to the ancient Japanese documents, the vowels of the four letters of kana -``烏````都`` ``奴``and ``布`` were pronounced in most cases like [u] and in very few cases like [o]. Some argue that (u) and [o] were interchangeable, but I have a different opinion, because it is certain that the (u) of the four Japanese ``Chinese characters, was the (u) of Korean, equivalents, before it had changed into (o). 3. The close study of the above-mentioned documents has revealed that the phonetic Sounds of Chinese characters used between the fifth and seventh centuries were not very different from those of Chinese characters we use today except for the prescriptive sounds like Tong-gukchongun, palatalization, and (z) sound.