Decolourization and COD removal from synthetic wastewater containing Reactive Brilliant Orange K-R (RBOKR) dye using sonophotocatalytic technology was investigated. Experimental results showed that this hybrid technology could efficiently remove the colour and reduce COD from the synthetic dye-containing wastewater, and that both processes followed pseudo first-order kinetics. At the condition of 0.1 m(3) h(-1) airflow, 0.75 g dm(-3) titanium dioxide and 0.5 mmol dm(-3) RBOKR solution, the rate constants of decolourization and COD removal were 0.0750 and 0.0143 min(-1) respectively for the sonophotocatalytic process; 0.0197 and 0.0046 min(-1) respectively for the photocatalytic process and 0.0005 and 0.0001 min(-1) respectively for the sonochemical process. The rate constants of sonophotocatalysis were greater than that of both the photocatalytic and sonochemical processes either in isolation or as a sum of the individual process, indicating an apparent synergetic effect between the photo- and sono-processes. (C) 2003 Society of Chemical Industry.