A mixture of polyphenol compounds (gallic acid, tyrosol, and syringic acid) is treated with ozone in water in the presence of activated carbon (AC). Individual (O-3) and combined (O-3/AC) ozonations have been carried out following the concentrations of initial compounds, intermediates, ozone, and hydrogen peroxide and total organic carbon (TOC). AC ozonation processes significantly improve both polyphenol conversion and mineralization. Hydrogen peroxide formed during the process seems to play an important role in accelerating the oxidation rate. Different carboxylic acids are formed as intermediate products. Consumption of ozone per unit mass of carbon removed is reduced in the combined ozonation process.