Abstract: An ozone generating unit comprises a number of dielectric tube and electrode assemblies bundled together in confronting contacting relationship, each dielectric tube and electrode assembly preferably comprising a number of concentrically related and spaced dielectric tubes. The ends of the dielectric tubes into which gas is to be ozonized is to flow terminate at different points located progressively axially inwardly thereof proceeding from the outermost to the innermost dielectric tube. An outer cylindrical conductive electrode is rigidly frictionally fitted over the outermost of the dielectric tubes. Supported on the inner surface of each dielectric tube is an inner cylindrical electrode made of a sheet of resilient flexible conductive mesh material initially deformed into a given curvature different from that of the cylindrical inner surface of the associated dielectric tube so that the inner cylindrical electrode expands into contact with the cylindrical inner surface of the associated dielectric tube.