In October 1899 the start of the Boer War between the Boer Republics and Great Britain witnessed Neumann returning to South Africa where he enlisted in the newly formed South African Light Horse. His knowledge of Africa and in particular his experience in the Zulu War meant that he was given the rank of lieutenant under the command of Colonel Julian Byng. Neumann served as part of the Mounted Brigade of the Natal Field Force under Lieutenant-General Douglas Cochrane, taking part in the relief of the besieged town of Ladysmith. He was also present at the Battle of the Tugela Heights and at a skirmish on Bastion Hill where according to J.G. Millais he was at the head of his troop. Neumann did not see out the end of the South African War returning to Britain sometime in 1901.