The Osterburg (German: [ˈoːstɐˌbʊʁk] ) is a castle located conspicuously on a hill in the middle of the town of Weida in the county of Greiz in the German state of Thuringia.

Its 54-metre-high bergfried is the third highest and one of the oldest surviving bergfrieds in Germany. Above its second array of battlements there is a watchman's parlour, which accommodated a watchman until 1917. On the terrace there is a monument which records that this was the furthest south that the ice sheet came in Germany during the Elster glaciation.

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• Henriette Joseph, Haik Thomas Porada (eds.): Das nördliche Vogtland um Greiz. (Landschaften in Deutschland Werte der deutschen Heimat, Vol. 68). Böhlau, Cologne etc., 2006, ISBN 3-412-09003-4.
• Rosemarie Bimek, Heinz Fischer, Roland Gehring, Dr. Egbert Richter, Kurt Häßner, Dieter Hauer, Günter Kummer: 800 Jahre Osterburg, Weida in Thüringen. Stadtverwaltung Weida in Thüringen, Heimatmuseum Osterburg, Altenburg, 1993, pp. 1–52.

• The Osterburg at Weida (Weida town website)
• Friends of the Osterburg Weida
• Initiative to save the tower spire
• Newspaper article about renovation work at the Osterburg, OTZ, 24 May 2011