This study examined the phonological phenomenon description aspect in Korean language textbooks published for Japanese learner during the modern period. The Korean language textbooks published from 1880 to 1940 were divided into five periods. In the 1880s, the principle of the occurrence of phonological phenomena was not accurately recognized, and it was explained in Japanese grammatical terms such as Onbin and Voiced sound. However, it was seen that the environment or process in which phonological phenomena gradually occurred was clearly recognized and described in later generations. From the 1911s to the 1920s, it describes the most types of phonological phenomena, and it can be seen that one phonological phenomenon is explained in detail. From the 1921s to the 1930s, the types of phonological phenomena dealt with in textbooks decreased in number but there were also textbooks that presented new phonological phenomena that were not covered in the previous period. It have been included in the textbook by newly identifying the phonological phenomenon that could not be identified in the previous period through research on the phonological phenomenon. From the 1931s to the 1940s, the phonological phenomena were dealt with in detail and considered the Korean language norms. The contents are very close to today's Korean language norms. Through this study, the diachronic changes in phonological phenomena in Korean language textbooks were examined thoroughly.