Max Rossteuscher was appointed as custodian of the National Museum of the Orange Free State, Bloemfontein, in June 1892, under the part-time curator Dr B.O. Kellner*. Though the museum had been established in 1877, Rossteuscher was the first suitably qualified full-time member of staff. His appointment meant that the museum could be opened to the public for several hours every day except Sundays. He expertly cared for the collections, provided useful information to visitors, and prepared a monthly list of new acquisitions for publication in The Friend, a local newspaper. The institution flourished under him and Kellner and was described in glowing terms by several South African newspapers. However, it suffered from a chronic shortage of funds and could pay Rossteuscher only ?120 per year. As a result he resigned in September 1893 to accept the better paid position of assistant curator at the State Museum (founded in 1892; later the Transvaal Museum) in Pretoria, under the honorary Director, Dr H.G. Breyer*.
At the State Museum Rossteuscher compiled a list of acquisitions by the museum to 30 December 1893 and had it printed. He and Dr Breyer prepared printed lists also for February, March and April 1894. However, Rossteuscher left the museum that same year. He was succeeded by Samuel M. Tweddill*. During 1915-1919 Rossteuscher was living in Kimberley.