In 1901, Matsui was admitted into the Army War College, an elite institution which accepted only about ten percent of annual applicants. Matsui was still taking classes there in February, 1904, when the College closed due to the outbreak of the Russo-Japanese War. He was immediately sent overseas where he served in Manchuria as a company commander in a combat unit of the 6th Regiment. During the Battle of Shoushanpu, he was wounded in action and most in his company were killed. At war's end, Matsui resumed his studies at the Army War College, and graduated at the top of his class in November, 1906.