Altes Palais, Royal palace in Darmstadt, Germany

Altes Palais was a neoclassical city palace on Luisenplatz, built 1802–1804, probably by Michael Mittermeyer. Its horseshoe-shaped plan had a three-story front with a slightly projecting three-bay bay and balcony, a mansard roof with dormers, and two-story side wings ending in square corner houses. It was demolished after World War II; the Luisencenter now stands on the site.

The palace was built between 1802 and 1804 under Landgrave Ludwig X of Hesse-Darmstadt as the first permanent city residence for the Hessian ruling family. After World War I and the abdication of the monarchy, it became the headquarters of the Hessian Finance Office.

The palace was the birthplace of Prince George Louis Victor Henry Serge of Battenberg, later George Mountbatten, on 6 December 1892. On 7 October 1903 Princess Victoria Alice of Battenberg married Prince Andreas of Greece there in a civil ceremony. Because of the family ties between Hesse-Darmstadt and the British royal house, English speakers called it the "Old Grand Ducal Palace".

The palace no longer exists; its site is now occupied by the Luisencenter at Luisenplatz 5, at the southern exit of Luisenplatz. The square and the nearby Alexanderpalais, built of reddish sandstone, remain visible. The location is on the former Wilhelminenstraße, one of Darmstadt's central north-south axes.

A member of the English royal family was born within these walls in 1892, connecting Darmstadt to major European monarchies. This connection made the building an important gathering place for high-ranking royal visits and family celebrations.