Mineralization of an anthraquinone dye, C.I. Reactive Blue 19 (RB19), by single ozonation, single sonolysis, and ozonation combined with sonolysis (O-3/US) was carried out in a laboratory-scale experiment. O-3/US treatment rendered a more effective result than the other two methods. The effect of several operational parameters, including initial dye concentration, pH, ozone dose, and ultrasonic energy density, on the reduction of total organic carbon (TOC) was also investigated. The concentrations of related anions (maleic acid, oxalic acid, acetic acid, formic acid, nitrite ion, nitrate ion and sulfate ion) and the ammonium ion during mineralization were detected by ion chromatography (IC) and the ammonia-Nessler's reagent colormetric method, respectively. Other carbon based intermediates (3,6-dinitrosocyclohexa-1,4-diene, aniline, phenol, benzo-1,4-quinoe, phthalic acid, butene diacid, oxalic acid, and acetic acid) were detected by gas chromatography/mass spectrometry (GC/MS). Based on the results of these analyses, we propose a possible degradation pathway of RB19 during the O-3/US process. (C) 2008 Elsevier B.V. All rights reserved.