The decomposition of ozone in water at different solution pHs in the absence or presence of activated carbons with different surface chemistries and textural properties was investigated. Activated carbon acts as a catalyst in the decomposition of ozone into radical species, significantly accelerating this process. Homogeneous and heterogeneous decomposition of ozone were described by second-order kinetic models. In general, both homogeneous and heterogeneous ozone-decomposition rates increase with solution pH. Textural and surface chemical features of the activated carbon play a role in the catalytic decomposition of ozone. Heterogeneous ozone decomposition is enhanced by activated carbon with high surface area and basicity. Despite the mild oxidation undergone by the activated carbon samples during ozonation, no strong deactivation occurs.