| Birth Date: | 2 December 1892 |
| Birth Place: | Pori, Finland |
| Death Date: | 17 June 1949 (aged 59) |
| Death Place: | Pori, Finland |
| Sport: | Swimming |
| Strokes: | breaststroke |
| Pb: | 100 m – 1:23.1 (1919) 200 m – 2:58.9 (1925) 400 m – 6:25.4 (1913) |
| Show-Medals: | yes |
Arvo Ossian Aaltonen (2 December 1892 – 17 June 1949) was a Finnish breaststroke swimmer who competed at the 1912, 1920 and 1924 Summer Olympics.[1] He won bronze medals in the 200 m and 400 m events in 1920, and failed to reach the finals in 1912 and 1924.
Aaltonen was the first, and until 1992, (with Antti Kasvio's bronze medal-winning 200m freestyle performance) the only Finnish Olympic medalist in swimming. He won the 200 m event at the 1923 Nordic Championships, and he held 22 Finnish titles: in the 100 m (1912, 1915–17), 200 m (1909, 1911–13, 1915–16, 1919–21, 1923, 1925–27) and 400 m (1912–13, 1915–17). In 1924–30 and 1946–47 he was a board member of the Finnish Swimming Federation. He immigrated to Canada in 1929, but returned to Finland in 1937.