Abstract: A tumbler plate cylinder lock having a hollow housing, a cylinder rotatably mounted into the housing, and a plurality of sheet-like locking members, or tumbler plates, snugly fitted in the cylinder. Each two locking members is interlocked by an arciform-shaped spring in such a manner that one extension of each locking member will be urged to extend out of a corresponding passage formed on the peripheral wall of a center bore of the cylinder and into a respective longitudinal slot formed on the inner peripheral surface of the housing, thus the cylinder is prevented from turning relative to the housing, whereby the cylinder lock is held in a locked position. Each locking member has a central opening for receiving a key having a shank provided with a plurality of depressions, and the central opening has a side wall provided with a projection to match a corresponding depression of the key shank.