Mönsterås Municipality, Administrative municipality in Kalmar County, Sweden.

Mönsterås Municipality is a municipality in Kalmar County, south-eastern Sweden, with its seat in the town of Mönsterås. Its area is mostly moraine covered with coniferous forest, with farmland mainly around the central town. The northern part is crossed by the river Emån, and the coastline runs for just over 150 km, fronted by an archipelago of some 300 islands larger than 0.5 tunnland, plus many smaller skerries.

The municipality was established in 1974 through the merger of three separate administrative areas, each with its own past. This consolidation shaped the current municipal structure that has remained unchanged for decades.

The municipal arms show the ridge where the town centre and its church have stood since the medieval age, and a cross for the Knights Hospitallers, a monastic order established in the town in the fifteenth century. The name Mönsterås derives from 'monastery' and 'ridge'. On Lövö, pollarding of lindens is still practised to maintain the landscape.

The E22 and national road 34 cross the municipality, and settlement followed the gravel ridges running from the inland to the Baltic. The coast stretches over 150 km, with more than 300 islands larger than 0.5 tunnland plus numerous skerries. Two of the islands, Lövö and Vållö, are nature reserves; Vållö, enlarged in 2020, covers Husön and about 80 islets.

The island world within the municipal area consists of hundreds of small and large landmasses forming a mosaic of nature and maritime life. This cluster of islands is a defining feature that sets the area apart from other Swedish regions.