The 2004 Brandenburg state election was held on 19 September 2004 to elect the members of the 4th Landtag of Brandenburg. The incumbent government of the Social Democratic Party (SPD) and Christian Democratic Union (CDU) led by Minister-President Matthias Platzeck was returned with a significantly reduced majority. The Party of Democratic Socialism (PDS) moved into second place, although polls prior to the election suggested it would become the largest party. The CDU fell to third place.

The Landtag of Brandenburg is the unicameral legislature of the state of Brandenburg in Germany. Its 88 members of parliament are usually elected every 5 years.