This article aims to introduce the textbooks and handwritten copies used by Goizumi Teizo, a Japanese military interpreter during the late Joseon Dynasty, whose collection is housed in the Harvard Yenching Library. Goizumi Teizo, under the name Hashimoto Akiyoshi before his adoption, came to Joseon under false pretenses and spent about 10 years learning Korean while engaging in espionage activities in Busan and the Jeolla region. In 1903, he temporarily returned to Japan due to his father’s illness, but when the Russo-Japanese War broke out, he returned to Joseon as a military interpreter, revealing his true identity and using the official name “Goizumi Teizo.” Over the next two decades, he served as an aide to 14 army commanders and retired in 1930. The books he owned were imported to Harvard University through a Japanese antiquarian bookstore in two installments in 1959. Until now, the names written in the handwritten copies were not standardized, making it difficult to ascertain their true owner. However, the author has identified them all, confirming that a total of 42 titles and 31 books were indeed part of Goizumi Teizo’s collection. These books have historical and linguistic value, as well as relevance to political and cultural studies. In this paper, I aim to provide a general overview of the characteristics of these books.