In the early First Millennium AD, Vietnam imported Chinese language and culture, which had a lasting influence ever since. Chinese influence on Vietnamese written and spoken language is notable in particular. Despite this, due to the fact the two languages belong to two distinct families and differences in the number and structure of syllables available in each language, the borrowed Chinese language cannot transcribe all of Vietnamese personal and local names properly. This is the reason for the formation of the Nom script. From the 17th century onwards, Western missionaries used the Nom script for religious purposes, which led to the formation of the Latin-based Vietnamese alphabet. It would not be an overstatement to say that, 17th century Catholic documents written in Nom are of indispensable value to researchers who wish to study the history of the Vietnamese language and the Latin-based Vietnamese alphabet. Based on the materials from Kinh nhung le mua phuc sinh (Scriptures on Easter Rituals), this paper will focus on the Nom transcription of foreign Saints' names, which will show the differences in syllabic structure between Western languages (Portuguese and France) and Vietnamese, as well as give an overall idea of Nom transcribing rules.