Lee Hye-ku(1909~2010) was the pioneer of Korean musicology whose academic orientation and methodology, which I term ‘mandanghak’ school, are still regarded as the most effective view in Korean musicology. Lee Hye-ku had no systematic musicological train at all and established his academic methodology by himself. Mandanghak was made both by the academic orientation of the time and Lee Hye-ku’s own persoanl experience. In this paper, I will explore the historical horizon or the textual horizon of the time and present horizon or scholar horizon of Lee Hye-ku’s own experience. I will discover how the two affect the establishement of Mandanghak school. Lee Hye-ku was born and raised in a prestigious family and is a born Confucianist. His scientific and positivism has transmitted by Seonghohak school established by Yi Yik (1681~ 1763). Yi, a Confucian scholar, admitted Western academism of open mind, diversity view, objectivity, and experientiality. The academic orientation of Seonghohak school has handed down to Lee. In this sense, the historical horizon for the establishement of Mandanghak school was Seonghohak school. Lee Hye-ku had not followed traditional education system but went to Japanese schools from elementary to college levels. His teacher at the English Literature Department of Kyojo Imperial University was Sato Kiyoshi (1885~1960) who emphasized the comparative study. The methodology was very popular among the scholars of the time. Lee Hye-ku accepted the methodology and wrote his first academic thesis comparing Korean traditional music with Chinese and Western musical theory. Lee Hye-ku was able to write his first thesis asked by Tanabe Hisao who was preparing a publication to dedicate his teacher Kishibe Shigeo. The connection between the three people was the Imperial University which was core of the academism of the time to raise the “elite of (Japanese) empire.” In this sense, Lee’s personal horizon was built up on the Imperial University. The essence of Mandanghak is inductive method, positivism and comparative view. The methodology of Mandanghak was most advanced and effective in the first half of the 20th century. However, it is not totally acceptable in this 21st century. We need to accept the advantage of Mandanghak, the open and scientific mind and discard the disadvantage, the tendency toward Western musicology and heavy positivism, in order to open an new era of Korean musicology.