Riddagshausen Abbey (Kloster Riddagshausen) was a Cistercian monastery just outside the city of Braunschweig in Germany.
It was founded as Marienzelle by Ludolf the Wend, a ministerialis of Henry the Lion and steward of Brunswick, and settled in 1145 by monks from Amelungsborn Abbey. Henry endowed the new foundation in 1146 with the neighbouring village of Riddagshausen, from which it took its name.
It was mediatised in 1569 by Braunschweig-Wolfenbüttel, when it became a Protestant establishment. From 1690 it was also the home of a prestigious Lutheran seminary for training of preachers, the first in Germany. The religious community and the seminary were dissolved in 1809.