Mareuil-sur-Ay (French pronunciation: [maʁœj syʁ aj], literally Mareuil on Ay) is a former commune in the Marne department in north-eastern France.

Since January 2016, Mareuil-sur-Aÿ is part of the administrative commune Aÿ-Champagne.

[3] Its vineyards are located in the Vallée de la Marne subregion of Champagne, and are classified as Premier Cru (99%) in the Champagne vineyard classification.

Together with Tauxières-Mutry it is the highest rated of the Premier Cru villages, and has therefore just missed out on Grand Cru (100%) status.

Regardless, the vineyards, harvest huts, presses, and cellars in Mareuil-sur-Ay were inscribed on the UNESCO World Heritage List in 2015 as part of the Champagne hillsides, houses and cellars site, because of the region's testimony to the development of champagne.