Prinsenkasteel, Medieval castle ruins in Grimbergen, Belgium.

Prinsenkasteel is a ruined castle beside a pond in Prinsenbos Park, Grimbergen. Its surviving masonry consists of a lower wall pierced by empty rectangular window openings and two round brick towers: the nearer one broader, the farther one slightly taller and narrower with small square openings near its top. The keep in the southwest corner and a round corner tower in the northwest, linked by the west facade, survived the 1944 fire.

The site was built in the 14th century as a residence for the Lords of Grimbergen and later served as a princely domain. It suffered significant damage during German occupation in World War II.

The name Prinsenkasteel recalls 1686, when Charles II of Spain granted Philippe-François de Glymes the title of Prince of Grimbergen, turning the castle into a princely estate. The Mérode family, who acquired it through the 1778 marriage of Charles de Mérode and Marie d'Ongnies de Mastaing, held it until 1959. The Guldendal, the former stables and carriage house, has housed the Museum of Old Techniques since 1982.

The castle ruins themselves are closed to visitors, but Prinsenbos Park around them is open to the public and has been managed by the Flemish Agency for Nature and Forestry since 2009. The ruins stand between Prinsenstraat, Guldendal, De Merodestraat, Speelbroek and Pastoor Woutersstraat. The Museum of Old Techniques in the nearby Guldendal is a separate visit.

The title of Prince of Grimbergen was granted in 1686 by Charles II of Spain to Philippe-François de Glymes, Count of Grimbergen, and the castle became a princely estate, hence its name. His tomb monument stands in the choir of the Sint-Servaasbasiliek in Grimbergen, on the gospel side.