A company of the regiment was removed from the unit and used for the formation of the 33rd East Siberian Rifle Regiment on 5 December 1903. From 1904 the 1st Siberian Rifle His Majesty's Regiment took part in the Russo-Japanese War as part of the 1st Brigade, 1st Siberian Rifle Division, 1st Siberian Army Corps. It fought in the Battle of Te-li-Ssu (14—15 June 1904), the Battle of Liaoyang (25 August—5 September 1904), and the Battle of Mukden (20 February—10 March 1905). After the losses at Te-li-Ssu some of the companies of the 1st Siberian Rifles only had about 150 to 160 fighting men left. It was upgraded with a third battalion on 2 February 1904 and later received another battalion on 11 October 1905. Two members of the regiment were awarded the Order of St. George, 4th class, for their service in the war against Japan. After the conflict the 1st Siberian Rifle Regiment was awarded with the St George's Banner with the label "For the battle of Mukden 21–26 February 1905" along with the silver cross of St. George with the label "For the battle of Liaoyang 17 and 18 August 1904", both on 26 November 1906.