This study looks at the remnants of Japanese language in Korean through synchronic and diachronic review focusing on idioms found in the Korean dictionary. These were compiled according to the times, looking at when and to what extent Japanese idioms have been used in Korean since the end of the 19th century. These attempts are thought to be recognized as academically valuable only when verified based on a vast amount of historical data such as novels and magazines. But, in this study, we analyze and examine the incorporation of Japanese language, albeit partially, into limited dictionaries and newspapers. Our results show that the number of Japanese idioms introduced into the Korean language dictionary during the Japanese colonial period was surprisingly small, however Japanese idioms were integrated rapidly after 1980. Therefore, it is believed that national countermeasures should be prepared in the future.