Abstract: A bendable, washable, watertight key switch assembly is disclosed to include a polymeric flexible top layer made, which has key caps and a conducting member respectively bonded to the inside wall of each key cap, a polymeric flexible bottom layer defining with the flexible top layer an accommodation space, and a thin film circuit board set in the accommodation space and sealed to the flexible top layer and the flexible bottom layer with an adhesive, the thin film circuit board having printed switch contacts corresponding to the conducting members in the key caps for the contact of the associating conducting members to output a corresponding electric signal and a cable electrically connected to the printed switch contacts and extended out of the flexible top layer and the flexible bottom layer at one side for connection to an external electronic device.