Until 1 January 2007 Sydthy municipality was a Danish municipality (Danish, kommune) in the former Viborg County on the west coast of Vendsyssel-Thy, a part of the Jutland peninsula in west Denmark.
The municipality covered an area of 322 km2, and had a total population of 11,239 (2005).
Its last mayor was Arne Hyldahl, a member of the Venstre (Liberal Party) political party.
It was merged with existing Hanstholm and Thisted municipalities to form a new Thisted municipality.
This create a municipality with an area of 1,072 km2 and a total population of 46,158 (2005).