Sigurd Frosterus (1876-1956) was a Finnish architect, art critic and art collector.
Frosterus had an architecture studio 1902-1904 with Gustaf Strengell and in 1918-1935 with Ole Gripenberg. Frosterus and Strengell drew villas and manor houses, including Tamminiemi, which later became one of the official residences of the President of Finland from 1940 until 1981.
Frosterus inspired numerous Finnish artists with his art theories and criticism. He collected post-impressionist art.
Frosterus was the editor of Arkkitehti magazine 1908-1911, and published books about art theory. He was a talented watercolour painter.
- Inkeroinen powerplant in Kymi 1923
- Vanajanlinna manor house, 1924
- Stockmann, Helsinki centre 1930
- Isohaara powerplant in Kemijoki 1949
- Helsingin säästöpankki, bank head office, 1932
- Yhdyspankki, bank head office, 1936
- "Frosterus, Sigurd". Biografiskt lexikon för Finland (in Swedish). Retrieved 8 January 2017.
- "Arkkitehtiesittely" (in Finnish). Museum of Finish Architecture. Retrieved 8 January 2017.
- "Art as an Attitude - The Sigurd Frosterus Collection". Visit Helsinki. Retrieved 8 January 2017.