Marugame Castle (丸亀城, Marugame-jō^?), also known as Kameyama Castle and Horai Castle, is a hirayamashiro (castle situated on a hill surrounded by a plain) located in Marugame, Kagawa Prefecture, Japan.

The first fortifications built on the site that would later become Marugame castle were erected by the Nara clan led by Nara Motoyasu, who in turn were retainers of the Hosokawa clan during the Muromachi Period. Little evidence of this exists today, however.

The roots of the current castle lie in 1587, when Marugame Castle was the residence of the lord of the Sanuki Province, Ikoma Chikamasa. In 1597, Chikamasa constructed Takamatsu Castle as his new location from which to rule from and turned Marugame Castle over to his son, Ikoma Kazumasa. Kazumasa immediately began renovating the castle, and made it into a formidable fortification. In 1615, however, due to a shogunal decree that each province could have but one castle, Marugame Castle was dismantled.

In 1641, a small section of western Sanuki (including what was left of Marugame Castle) was granted, as a fief, to Yamazaki Ieharu for his valor in the 1638 Shimabara Rebellion. Ieharu re-built the castle on the ruins of the original and most of what stands today dates from his reconstruction, which he completed in 1644. However, in 1658, the castle was turned over to the Kyōgoku clan. They further improved the castle by rebuilding the Otemmon complex in 1670. The Kyōgoku managed to retain control of the castle until the Imperial Government seized control of it during the Meiji Restoration.