Mariental Abbey (German: Kloster Mariental) in the present Mariental in Lower Saxony, Germany, is a former Cistercian monastery founded in 1138, along with Marienberg Abbey in Helmstedt, by Pfalzgraf Friedrich II von Sommerschenburg. It was a daughter house of Altenberg Abbey of the filiation of Morimond. The initial complement consisted of twelve monks from Altenberg under an abbot (Bodo) from Amelungsborn Abbey. In 1179 the von Sommerschenburgs died out and the monastery with its possessions fell into the hands of Henry the Lion.