Nienburg (German: [ˈniːnˌbʊʁk] ⓘ) is a town in the district of Salzlandkreis in Saxony-Anhalt, Germany.

The medieval centre of the town is occupied by the Benedictine monastery, Nienburg Abbey, later turned into a castle, recently destroyed by fire.

The church of the monastery, over 1000 years old, was inaugurated in 1004, and is beautifully preserved to this day.

In 1623, during the Thirty Years' War, part of the town was destroyed.

A contributing factor may have been youths attempting to get the bridge to sway to the tune of "God Save the King.