Lee Hye-ku (also known by the pen name, Mandang) made great achievements in various fields, such as the history of Korean music, Korean musical theory and bibliography. Among many of his achievements, this study discusses his achievement in research on classical music note and its meaning. The discussion explores the contents of study on classical music notes divided into the study on interpretation of time value with classical music notes and rhythm, musical tone/structure and study on melodies, music notation, translated notes and annotation, etc., focusing on summarizing their meanings and his achievements. In his study on classical music notes, the greatest emphasis is thought to have been put on the interpretation of time value in Jeongganbo (Korean traditional music score) and study on its rhythm. Mandang’s study on the time value in Jeongganbo and interpretation of its subject, issues regarding the interpretation of time value in non-Jeongganbo, relationship between Jeongdan/Daegang and beat types and issues regarding tempos is believed to be the fruit and core of study on classical music scores. Mandang approached his study on classical music scores from various aspects. In addition to the interpretation of time value in Jeongganbo and the issue of beat, he comprehensively handled tone, structure, melodic structure with regard to melodies implied in classical music scores. His study led to making achievements in diachronic understanding on connection between the past music contained classical music scores and the present. His achievements in classical music scores were very extensive, covering the issue regarding interpretation of Jeongganbo, analysis of tunes, chronical review of music notation and scores for classical music scores, and translated musical annotation and notes of classical music scores. The results of his study provided a solid insight into outlining the trend of Korean music history through literature and laid a foundation on the theory of Korean music.