The remains of a Henrician artillery castle, built around 1541, by Henry VIII as part of his network of coastal defences to protect against French and Spanish attacks. It was erected together with Portland castle to defend the anchorage between Weymouth and Portland. The castle was repaired in 1548 and again in 1610/11and bastion earthworks were probably added then. They were noted on the 1623 survey. The castle was in Royalist hands during the English Civil War before it was abandoned in 1644-5 as it was of no military importance. It was then used as a storehouse until at least 1691. During the Second World War an anti-aircraft battery was probably positioned at the castle.
Sandsfoot Castle is now located within the 19th century breakwater of Portland harbour, the castle has suffered erosion from the sea and the remains are unsafe, but can be viewed from the surrounding fence and the shore.