This article examines the system of thought concerning Park Un's philosophy of self-cultivation, based on one of his two main works, Gyukmongpyeon.
 Park Un was a representative scholar of Neo-Confucianism from the Gyeongbuk Seonsan region during the middle period of the Joseon Dynasty. He gained widespread recognition for his filial devotion to his parents. He studied under Park Young along with the Kim brothers, Kim Chwiseong and Kim Chwimun, contributing to the nationwide prominence of the Songdang school of thought. However, following the last wishes of his father, Park Jongwon, who had witnessed the tyrannical rule of King Yeonsan and the political chaos during King Jungjong's reign, he did not pursue a career in government. Instead, he stayed in his hometown, dedicated himself to scholarly pursuits, and worked to pass down his academic achievements to future generations. He also gained fame as a great scholar of his time through interactions and academic discussions with contemporary scholars like Lee Eonjeok and Lee Hwang.
 At the age of 50 (in 1542), Park Un compiled Gyukmongpyeon by selecting various sayings from the Cheng-Zhu school of Confucianism centered around Cheng Yi and Zhu Xi, focusing on ‘Geo Gyeong Gung Ri’. ‘Geo Gyeong’ refers to a self-cultivation method that targets the heart-mind to foster virtue, while ‘Gung Ri’ refers to a study method targeting principles to explore all things and expand knowledge. These two elements collectively indicate the self-cultivation philosophy of the Cheng-Zhu school that needs to be integrated to prevent the human mind from falling into desire.
 Lee Yulgok wrote in the postscript of Gyukmongpyeon: “Only after reading Master Park Un's Gyukmongpyeon did I realize how deep his research into the self-cultivation theory of the Cheng-Zhu school was, and how diligently he had studied. Had that not been the case, the sentences he selected could not have been so precise and heartfelt.
 Although we can't meet t he v arious masters o f the C heng-Zhu s chool today, Park Un has gathered all their beneficial teachings left for future generations. The grace he has bestowed upon future scholars is indeed immense.” Through compiling Gyukmongpyeon, Park Un not only succinctly and clearly organized the self-cultivation philosophy of previous sages but also significantly contributed to the scholarly activities of future generations.