This study investigates Sino-Japanese and Sino-Vietnamese cognates listed in the Old JLPT Vocabulary List and examines their relevance for Japanese language education. Focusing on kanji-only vocabulary, it extracts and classifies one- and two-character items and analyses correspondences in written form, core meaning, and grammatical function. Using dictionarybased comparison supplemented by checks from highly proficient native Vietnamese speakers, the study identifies many same-form cognates, particularly in academic, administrative, scientific, and abstract domains. It also shows that about 18.8% of same-form two-character items exhibit part-of-speech mismatches, such as noun–adjective and noun–verbal noun correspondences, which may lead to negative transfer. Overall, the findings indicate both the pedagogical value of same-form cognates and the need for instructional approaches that account for grammatical differences.