Hôtel d'Aux, Neoclassical private mansion in Nantes, France.

Hôtel d'Aux is a neoclassical mansion built of granite and tuffeau with a slate roof, at the corner of Place Maréchal-Foch and Rue Tournefort. Its south-facing facade has seven bays, the middle three projecting under a triangular pediment carved with two wild men flanking a shield. A continuous iron balcony runs across the middle level, and a round-arched blue door opens at the base.

Jean-Baptiste Ceineray, Nantes' architect from 1770, built the hôtel d'Aux between 1771 and 1774 as the first building on the new place d'Armes, for René Louis d'Aux (1707-1780), a white Creole from Saint-Domingue who owned slaves and plantations there. From 1800 to 1828 it housed the prefects of Loire-Inférieure; Napoleon I, Josephine, Talleyrand and Decrès were received there in 1808. During the Occupation it held the Feldkommandantur of Karl Hotz, shot on 20 October 1941. The army left in 2011 and it became a private residence, listed on 7 February 2012.

The triangular pediment bears two carved "wild men" flanking a shield meant to hold the owner's coat of arms, a decorated pediment that is unusual for 18th-century Nantes buildings. The white marble fireplaces and the grand salon are listed with the facades. The building became a private residence after the army left in 2011.

The mansion is located at the intersection of Place du Maréchal-Foch and Rue Tournefort in central Nantes, making it easy to find. As a protected monument, it is not open for public visits inside, but the exterior facade can be admired from the street.

In March 2019, work on the Line 4 e-busway power station uncovered a walled-up tunnel under Rue Tournefort linking the hôtel to the Saint-Félix tunnel. Local historians knew of it; it is thought the Germans could have used it to leave the building unseen and reach a boat kept moored in the tunnel.