Rantasalmi () is a municipality of Finland. It is located in the South Savo region, northwest of Savonlinna and northeast of Mikkeli. The municipality has a population of () and covers an area of of which is water. The population density is .
Neighbouring municipalities are Joroinen, Juva, Savonlinna, Sulkava and Varkaus.
The municipality is unilingually Finnish.
Asikkala, Osikonmäki, Putkisalo, Rantasalo, Torasalo, Tornioniemi, Tuusmäki and Vaahersalo.