Royal abbey of Saint-Nicolas-aux-Bois, Benedictine abbey ruins in Saint-Nicolas-aux-Bois, France.

Abbaye de Saint-Nicolas-aux-Bois is a Benedictine abbey in a rural valley setting, of which a square tower and the abbot's residence remain visible today. These structures display architectural elements from the 15th century.

Founded around 1086 by two hermits during the reign of King Philip I, the abbey became a double monastery of monks and nuns. Abbot Simon of Saint-Nicaise de Reims imposed a reform from 1120 to 1134. In 1403 an English archer killed the abbot, and in 1418 the English pillaged and ruined the abbey; Protestants destroyed it again in 1567. Rebuilt from 1722 to 1738 and in 1764, it was suppressed on 13 February 1790 and sold as national property.

In the 13th century Enguerrand IV, sire de Coucy, had three students of the abbey executed. King Louis IX condemned him to make amends on the site of the crime for 13 days.

The site is protected as a registered historic monument and can be explored via walking paths through the surrounding countryside. Visitors can view the ruins freely while enjoying the rural landscape at their own pace.

In 1761 the abbey's conventual mensa drew income from six farms, three houses and a mill at Saint-Nicolas, while the abbot's mensa held six more farms and a mill at Molinchart. The abbey also collected tithes from twelve parishes, including Faucoucourt.