The 2009 Brandenburg state election was held on 27 September 2009 to elect the members of the 5th Landtag of Brandenburg. It took place on the same day as the 2009 federal election and 2009 Schleswig-Holstein state election. The incumbent government of the Social Democratic Party (SPD) and Christian Democratic Union (CDU) led by Minister-President Matthias Platzeck took small losses, but retained a majority. However, the SPD chose to form a government with The Left rather than continue the SPD–CDU coalition.

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.