Rantasalmi is a municipality of Finland. It is located in the Southern Savonia region, 43 kilometres (27 mi) northwest of Savonlinna and 92 kilometres (57 mi) northeast of Mikkeli. The municipality has a population of 3,261 (31 October 2024) and covers an area of 925.20 square kilometres (357.22 sq mi) of which 366.61 km2 (141.55 sq mi)
is water. The population density is 5.83 inhabitants per square kilometre (15.1/sq mi).
Neighbouring municipalities are Joroinen, Juva, Savonlinna, Sulkava and Varkaus.
The municipality is unilingually Finnish.