The degradation of Rhodamine B dye was evaluated under different radiation conditions: sonolysis, photolysis, sonocatalysis, photocatalysis, and sonophotocatalysis, where commercial TiO2 was utilized as catalyst. Color removal was monitored by spectrophotometry and mineralization was determined by TOC analysis. A two-first-order in-series reactions model was developed; it takes into consideration reaction times where the intermediates prevail. In this reaction scheme, the first reaction is the degradation of the coloured dye into coloured intermediates, and the second reaction is the conversion to colorless products. Good agreement was observed between experimental data and the developed kinetic model. The results suggest that dye degradation rate is more than one order of magnitude larger than the corresponding one for coloured degradation of intermediates. Under experimental conditions considered, water-soluble materials predominated over mineralized products within colorless products.