Social Democratic Union

Social Democratic Union may refer to:


 * Social Democratic Union (Croatia)
 * Social Democratic Union (Ireland), started by Tommy Broughan in 2014 after he left the Labour Party
 * Social Democratic Union (Latvia)
 * Social Democratic Union (Serbia)
 * Social Democratic Union (Romania)
 * Social Democratic Union (Ukraine)
 * Social Democratic Union of Macedonia
 * Social Democratic Union of Workers and Smallholders, a political party in Finland
 * Social Democratic Union 'Proletarian', a political party in Bulgaria
 * Social Democratic Unionists, a political party in Syria
 * Polish Social Democratic Union, defunct political party in Poland