Old Keiss Castle is a partially ruined castle in Scotland, overlooking Sinclair's Bay near Keiss village. Built in the late 16th or early 17th century by George Sinclair, it was later replaced by Keiss House around 1755. The castle features a Z-plan tower house with corner towers and a vaulted basement. Despite its ruinous state, the castle holds historical significance and is protected as a scheduled monument.