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.

[2] 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).

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