Château de la Leonardsau, Listed historical monument in Obernai, France.

Château de la Leonardsau is a multi-part building of cream stucco and brown stone trim under steep red tile roofs, with a half-timbered gable over an arched entrance and a carved stone relief between two upper windows. It stands at the lieu-dit Saint-Léonard on the land of Obernai, close to Boersch. Its eight-hectare park, laid out by Belgian landscaper Jules Buyssens with the baron, mixes English, French, Italian and Japanese garden elements.

Baron Albert-Louis-Eugène de Dietrich bought the estate in 1896 and built the present castle in stages: the central villa in 1899–1900, the west wing in 1909–1910, and the east wing in 1921 for the marriage of his niece, Mlle Oesinger. The ensemble was built in the Renaissance taste with many reused elements. The town of Obernai bought the domain in 1970.

Charles Spindler decorated one salon in 1902 with Art Nouveau elements that remain part of the room's character today. This artistic work shows how international art movements shaped the taste of the local upper class.

The park covers eight hectares and was laid out by Belgian landscape architect Jules Buyssens together with Baron de Dietrich, combining English parkland, a French garden and small Italian and Japanese garden scenes. Edouard André also worked on the grounds. The castle reopened to the public on 1 November 2025 after restoration begun in 2023.

The 1971 film 'La Décade Prodigieuse' starring Orson Welles, Marlene Jobert, and Anthony Perkins was filmed on the castle grounds. This Hollywood connection shows how the location attracted international film productions.