A study of the ozonation of distillery and tomato wastewaters was carried out in a small bubble contactor in order to obtain kinetic data for scaling-up. Thus, several parameters, such as chemical oxygen demand (COD), 254 nm absorbance (AJJ,) and organic carbon content (OC), were followed during ozonation at different experimental conditions.For distillery wastewaters all parameters investigated have the highest decreases during the first minutes of ozonation, A^ showing the highest disappearance rates. Thus, during the first Fifteen minutes of ozonation an important decrease of the 254 nm absorbance (~ 75%) was observed. At further reaction times values of all parameters studied decrease slowly, eventually reaching a plateau value. During approximately the first two hours of reaction, dissolved ozone was never found, which suggested that fast or moderate gas-liquid reactions took place in the wastewaters.Regarding tomato wastewaters, COD, OC and A^ reach reductions of up to 70%, 40% and 90%, respectively, in one hour of ozonation. In this case the presence of dissolved ozone suggested that the kinetic regime of ozone absorption corresponded to a slow reaction.Application of an ozone balance in gas and water phases, along with the kinetic equation for ozone absorption with chemical reaction lead to determination of physico-chemical parameters like Henry's law constant and reaction rate coefficient, e 03 . In spite of the limitations concerning actual values of mass transfer coefficient, specific interfacial areas and ozone diffusivity, the rate coefficient obtained was found to be independent of hydrodynamic conditions, although it diminished with reaction time. This, however, was in agreement with the changing nature of the wastewater content. 355