Abstract: A corona discharge ozone generating apparatus comprises a plurality of plate-like electrodes arranged in a stack. Alternate ones of the electrodes are electrically earthed, hollow and have a fluid medium passed therethrough for cooling. The remaining electrodes are each mounted on respective insulating frames sandwiched between two plates of dielectric material. Each frame, and the electrode and dielectric plates which are carried thereby, bound a pair of discharge spaces in which ozone is generated and the frame includes two end portions which hold the electrode and plates, one end portion having holes therein communicating with the interior of a housing in which the stack is located so as to admit air or oxygen gas to the interior of the discharge space while the other end portion has openings therein communicating with a conduit for removing generated ozone from the housing.