During the Russo-Japanese War of 1904-1905 Kornilov became the Chief of staff of the 1st Infantry Brigade, and was heavily involved in the Battle of Sandepu (January 1905) and the Battle of Mukden (February/March 1905).
Pada Perang Rusia-Jepang 1904-1905, Kornilov menjadi Ketua staf Brigade Infanteri ke-1, dan sangat terlibat dalam Pertempuran Sandepu (Januari 1905) dan Pertempuran Mukden (Februari/Maret 1905).