The Treaty of Fredrikshamn (Swedish: Freden i Fredrikshamn; Russian: ), or the Treaty of Hamina (Finnish: Haminan rauha), was a peace treaty concluded between Sweden and Imperial Russia on 17 September 1809. The treaty concluded the Finnish War and was signed in the Finnish town of Hamina (Swedish: Fredrikshamn). Russia was represented by Nikolai Rumyantsev and David Alopaeus (Russian ambassador to Stockholm), while Sweden by Infantry General Kurt von Stedingk (former Swedish ambassador to Petersburg) and Colonel Anders Fredrik Skjldebrand.In the treaty, Sweden ceded Finnish territories to Russia.

The Finnish War (Swedish: Finska kriget, Russian: Финляндская война, Finnish: Suomen sota) was fought between the Kingdom of Sweden and the Russian Empire from 21 February 1808 to 17 September 1809. As a result of the war, the eastern third of Sweden was established as the autonomous Grand Duchy of Finland within the Russian Empire. Other notable effects were the Swedish parliament's adoption of a new constitution and the establishment of the House of Bernadotte, the new Swedish royal house, in 1818.