Ekebyholm Castle, Castle building near Lake Syningen, Norrtälje Municipality, Sweden

Ekebyholm Castle is a castle-like mansion and former manor on a peninsula in Lake Syningen in Rimbo parish, Norrtälje Municipality. Its main building has a strict Carolinian appearance with a säteri roof, high first-floor windows and a double staircase leading to the entrance portal, above which the coats of arms of Arvid Horn and Margareta Gyllenstierna are visible. The castle and its wings now serve as dining hall and boarding house for Ekebyholmsskolan.

The Oxenstierna family acquired the estate in the 17th century, and Bengt Bengtson Oxenstierna began building the original manor house. From 1932 onwards, an Adventist educational institution took over the building and has run it as a school ever since.

The name Ekebyholm is first recorded in 1409, when a document mentions "rangwaster j ekeby". Since 1932 the Adventist community has run Ekebyholmsskolan on the estate; the castle and its wings now serve as dining hall and boarding accommodation, while the 1802 library building has been restored for school use.

The grounds can be explored on foot along maintained paths that run beside the lake and through the wooded parts of the property. As the castle functions as an active school, access to the interior of the building is generally not open to outside visitors.

Although the building has been used as a school for nearly a century, the original manor structure remains largely intact and clearly readable from the outside. The Adventist community that has run the property since 1932 is one of the few religious groups in Sweden to operate a historic manor as a working school.