Abstract: An anti-rotation system for an interstage seal located in a gas turbine engine of a type having a turbine section including a first stage disk having a rearwardly extending aft shaft and a second stage disk. The interstage seal includes a rearwardly projecting conical arm mounted on the first stage disk. The interstage seal anti-rotation system includes a key inserted within an opening formed between the aft shaft and the conical arm for preventing circumferential movement between the aft shaft and the conical arm by providing a double shear plane between the aft shaft and the conical arm. A circumferential wire is inserted within a slot formed in the conical arm and a groove on the key for preventing axial movement of the key.