Herzberg Castle (German: Schloss Herzberg) is a German schloss in Herzberg am Harz in the district of Osterode am Harz in the state of Lower Saxony. The present-day, quadrangular building has its origins in the 11th century as a medieval castle. After a fire in 1510 it was rebuilt as a schloss and is one of the few in Lower Saxony that was constructed as a timber-framed building. Because it belonged to the House of Welf for 700 years it is also known as the Welf Castle of Herzberg (Welfenschloss Herzberg).