Sandemar Nature Reserve (Swedish: Sandemars naturreservat) is a nature reserve in Stockholm County in Sweden. The nature reserve lies close to Sandemar Castle and the landscape is characterised by having been part of the manorial estate for a long time. The area is considered to be one of the foremost examples in Stockholm County of such a landscape. It includes coastal meadows rich in bird-life and a rich fen situated in the eastern part of the reserve.