At an early age, he learned the Chinese classics from his father and his maternal grandfather, Yi Gyeong-jik.

In 1870, at age fourteen, Yu joined the circle of Park Gyu-su who was also a trusted friend of the late Crown Prince Hyomyeong, a leading scholar of Bukhak (북학; 北學; lit.

[2][3] The movement advocated for learning from abroad in order to reform the country, which was an unconventional idea in Joseon at the time.

[2] When the Imo Incident occurred in 1882, Min Yeong-ik [ko] recommended that Yu return to Korea, which he did in January 1883.

[2] In July 1883,[2] Yu traveled as an attendant to Min as part of the first-ever Korean special mission to the United States.

He stayed for around a year and a half thanks to the patronage of the American zoologist Edward S. Morse, whom he had previously met while in Japan.

[2][3] However, upon his return to Korea, he was viewed with suspicion due to his association with members of the pro-reform Gaehwa Party.

[2] While in detention, Yu wrote a book on his experiences entitled Observations on Travels in the West (서유견문; 西遊見聞; Seoyu Gyeonmun) and published it in 1895.

The book is nearly 600 pages long,[4] and is written in a mix of hangul and hanja, and introduces Western civilization to Korean audiences.

[2][4] At the end of the Donghak Peasant Revolution and the First Sino-Japanese War that followed, Yu worked in the government as part of a pro-Japanese faction.

[a][1] In October 1895, he was labeled by King Gojong as one of the 'Eulmi Four Traitors' for collaborating with Imperial Japan leading up to the assassination of Empress Myeongseong.

Following the assassination, Yu contacted Inoue Kaoru, the Japanese Minister for Foreign Affairs, to discuss the incident.

In February 1896, during Gojong's internal exile to the Russian legation, the pro-Japanese faction collapsed, and Yu fled to Japan.