Alzey Castle, Medieval castle in Alzey, Germany.

Alzey Castle is a rectangular castle complex at the eastern edge of Alzey's old town, rebuilt around 1905 on the ruins of an earlier castle. Its east side has a thick wall toward the former open land, while the west side borders the town wall around a courtyard with two portals. The south wing, the Friedrichsbau, now serves as a girls' boarding school; the north wing houses the Philipps- and Ludwigsbau, used by the district court. A thick round cannon tower stands at the southwest corner, and a gate tower at the northwest corner was the only entrance from the outer courtyard.

The castle was founded in the 13th century as the seat of the Rhenish Palsgraviate, serving as a residence for several Palsgraves including Ruprecht II and III. It suffered heavy damage during the Palatine War of Succession at the end of the 17th century and was rebuilt in the early 20th century.

The castle's name lives on in the street Schlossgasse, where the district court sat from its founding in 1879 in the former Burggrafiat at number 11. The site also hosts the Da Capo! festivals, and part of the rebuilt complex serves as a boarding school for girls.

The castle stands at the eastern edge of Alzey's old town, where the outer bailey once adjoined the town wall. The complex is now used by the Alzey district court, the boarding school of the Alzey grammar school and the Da Capo! festival, so the courtyards and buildings are not freely open to visitors. The Schlossgasse and the area around the former Burgrafiat at Schlossgasse 11 give the best view of the gate tower and the round cannon tower.

The court that occupies the rebuilt castle is not a newcomer: the Alzey district court was founded in 1879 and first sat in the former Burggrafiat at Schlossgasse 11. Around 1900 the state chose the ruin itself as the site for new court, tax office and district treasury buildings, which is why Karl Hofmann rebuilt it in 1901–1903 instead of selling it to the town.