Rantasalmi is a municipality of Finland. It is located in the Southern Savonia region, 43 kilometres northwest of Savonlinna and 92 kilometres northeast of Mikkeli. The municipality has a population of 3,295 and covers an area of 925.20 square kilometres of which 366.61 km2 is water. The population density is 5.89 inhabitants per square kilometre. Neighbouring municipalities are Joroinen, Juva, Savonlinna, Sulkava and Varkaus. The municipality is unilingually Finnish.