Annanguo yiyu 安南國譯語is an edition of Annan yiyu 安南譯語 , a 16th-century Vietnamese lexicon that transliterates Vietnamese vocabularies using Chinese characters. As the earliest recorded systematic Vietnamese lexicon, it is indispensable in reconstructing the phonological history of Vietnamese. This paper romanizes all the Vietnamese pronunciations recorded in Chinese characters in Annanguo yiyu and works out tonal correspondences between Vietnamese and Chinese characters. The tonal characteristics of pre-modern Vietnamese are inferred from the Dictionarium Annamiticum Lusitanum et Latinum (1651). By comparing these with early Mandarin Chinese phonological works , such as Zhongyuan yinyun 中原音韻 , Hebing zi xue jiyun 合併字學集韻 , as well as with modem Mandarin dialects, we find that pronunciations in Annanguo yiyu reflect the main tonal values of Chinese topolects at the time: the yinping 陰平was a middle-level tone; the yangping 陽平was a low tone; the shangsheng 上聲was a falling tone; and the qusheng 去聲was a high-rising tone . In addition, the rusheng 人聲stop consonants had already disappeared from the language, while sometimes producing variations in pronunciation reflecting different strata of literary and colloquial readings 文白異讀.