After the graduation, Yi returned to Korea and was appointed as Captain.

But he was removed on 15 October 1900 when he told secrete of the country to a Japanese.

But on 7 June 1904, during the Russo-Japanese War, Yi returned to office.

At the same time, Yi became the headmaster of Military Academy of Korean Empire.

On 13 April 1905, Yi was promoted to colonel, and major general on 13 December 1905.

On 15 February 1906, Lee awarded 3rd class of Order of the Palgwae.

On 3 September 1907, Yi removed all the personnels of Imperial Korean Army who does not have any position.