Altleiningen Castle, Medieval castle in Altleiningen, Germany.

Altleiningen Castle is a ruined hill fortress on a rocky spur above the Eckbach valley, built around 1100–1110 by Counts Emich I and Emich II of Leiningen. Its triangular plan follows the hilltop; the outer ward had its own moat and was separated from the main castle by a rock-cut ditch crossed by a drawbridge. The surviving southeast palas wall with three rows of windows was rebuilt after 1962, and a youth hostel now occupies part of the site.

Altleiningen Castle was probably built around 1100 to 1110 by Count Emich I of Leiningen and his son Emich II under the name Leiningen Castle. It was first destroyed in the Peasants' Revolt of 1525 and rebuilt in Renaissance style from 1528 by Counts Cuno II, Philip I, Louis and John Casimir. French troops destroyed it for good in 1690 during the War of the Palatine Succession.

The name comes from the Leiningen counts; the prefix Alt- (old) was added after Neuleiningen was founded 5 km northeast. Since 1980 the amateur Burgspiele Altleiningen theatre troupe has performed classical and modern plays each summer in the covered Ehrenhalle, which seats about 220–250 spectators. The Rittersaal now serves as the youth hostel dining room, and the Burgschänke pub has a summer terrace.

The castle stands at 283 metres on the eastern spur of the Ameiser, above the left bank of the Eckbach. The outer ward was once cut off by a main ditch hewn from the rock, crossed by a drawbridge; that ditch now serves as a public open-air swimming pool. The covered Ehrenhalle has around 220 seats and hosts the Burgspiele theatre in summer.

The castle cellars are home to one of the largest bat colonies in Germany, a fact that has made the site an officially protected animal habitat. The bats are not visible when the cellars are closed, but information panels on site explain their presence and the measures taken to protect them.