Aya Castle is a castle located in Aya, Miyazaki Prefecture, Japan. Aya was built from around 1331 to about 1334. Its name derives from the man who over-saw the construction of the castle, who referred to himself only as "Aya". His family ruled over the castle until the Muromachi period, when the head of the Itō clan took over Aya Castle. The Shimazu clan seized the castle following their victory over the Itō in 1577.
The castle was then given to Niiro Hisatoki, one of the retainers for the Shimazu Clan. Toyotomi Hideyoshi conquered the castle for a short period ten years later. In 1615, however, the castle was destroyed due to a shogunal decree that every domain could have only one castle. The castle keep, or tenshu, was rebuilt in 1985 out of wood, and was based on pictures of other castles of the era. It houses a museum that has items pertaining to the castle's history.