Guldborgsund is a municipality (Danish, kommune) in Region Sjælland in Denmark, created on 1 January 2007 from six (6) former municipalities on the two islands Lolland in the west and Falster in the east bordering the Guldborgsund strait. It covers an area of 903.15 km² (2013) and has a total population of 61,007 (1 January 2014). Its neighboring municipalities are Lolland to the west and Vordingborg to the north. Its administrative seat is in the town of Nykøbing Falster. Its mayor as of 2010 is John Brædder from the local party New Guldborgsund.
On Monday January 1, 2007 Guldborgsund municipality was created as the result of Kommunalreformen ("The Municipal Reform" of 2007), consisting of the six (6) former municipalities of Nykøbing Falster (located partly on the island of Falster and partly on Lolland (its Sundby section)), Nørre Alslev (Falster), Stubbekøbing (Falster), and Sydfalster (Falster) and two former municipalities located on the island of Lolland: Sakskøbing and Nysted.
The largest company headquartered in the municipality is Codan Medical in Nysted, although its activities are actually concentrated in Rødbyhavn in neighbouring Lolland Municipality.
Coordinates: 54°46′11″N 11°52′57″E / 54.769722°N 11.8825°E