Published in 1999 in No. 28 of Tōnan Ajia: Rekishi to Bunka (東南アジア―歴史と文化―, Southeast Asia: History and Culture), this Japanese-language article by Shimizu Masaaki (清水政明) is titled “Sino-Vietnamese Readings Included in the Dictionary of Alexandre de Rhodes” (Alexandre de Rhodes の辞書に見るベトナム漢字音について). The study uses Alexandre de Rhodes’s Dictionarium Annamiticum Lusitanum et Latinum—commonly known as the Vietnamese–Portuguese–Latin Dictionary, published in Rome in 1651—as its principal source for investigating the history of Sino-Vietnamese pronunciation. From the perspective of historical phonology, the article analyzes more than 970 Chinese characters transcribed in Romanized Vietnamese with diacritics in de Rhodes’s dictionary. By comparing these seventeenth-century transcriptions with modern Sino-Vietnamese readings, the author examines changes in the system of initial consonants, consonant clusters, vowels, final consonants, and tones, thereby illuminating features of Middle Vietnamese and the historical development of the modern Sino-Vietnamese reading system. An important part of the study concerns changes in consonants and consonant clusters between the seventeenth and twentieth centuries. The author analyzes cases in which the readings recorded by de Rhodes differ from modern Sino-Vietnamese pronunciations and argues that some of these differences reflect systematic processes of phonological change. The study also indicates that certain older forms did not disappear completely but remain preserved in some present-day Vietnamese dialects, demonstrating the value of seventeenth-century materials for investigating both the history and dialectal diversity of Vietnamese. The article also investigates the Vietnamese tonal system documented in de Rhodes’s dictionary. Although the seventeenth-century system contained six tones, as does modern Vietnamese, the author observes that some syllables written with the hỏi tone in modern orthography were recorded with the ngã tone in the seventeenth-century dictionary, and vice versa. This phenomenon is considered in relation to register distinctions and the historical development of Vietnamese tones. More broadly, the study demonstrates that Alexandre de Rhodes’s Vietnamese–Portuguese–Latin Dictionary is not only an important source for the history of Quốc Ngữ, but also a particularly valuable linguistic resource for reconstructing seventeenth-century Vietnamese and the historical development of Sino-Vietnamese readings. Comparing the dictionary’s transcriptions with modern Sino-Vietnamese pronunciation reveals phonological changes that unfolded over several centuries, while also providing evidence for the influence of dialectal variation and naming taboos on certain readings. The article is therefore valuable for research on Vietnamese historical phonology, Sino-Vietnamese readings, dialectology, the history of Quốc Ngữ, and the historical development of the Vietnamese language.