Kinetic data obtained from a number of different investigators on the reaction of S(IV) with ozone in aqueous solution have been analyzed in terms of a single self-consistent rate expression. The rate expression that most appropriately fits all kinetic observations treated in this study is: − d[ S( IV)]/ dt = ( k 0 α 0 + k 1 α 1 + k 2 α 2)[ S( IV)][ O 3] where α 0, α 1, and α 2 denote the fraction of S(IV) in the form of SO 2·H 2O, HSO − 3 and SO 2− 3, respectively. This kinetic expression is similar in form to the empirical rate laws reported by Erickson et al. (1977, Atmospheric Environment 11, 813–817) and Hoigne et al. (1985, Water Res. 19, 993–1004). The recommended values for k 0, k 1 and k 2 are (2.4 ± 1.1) × 10 4 M −1 s −1, (3.7 ± 0.7) × 10 5 M −1 s −1, and (1.5 ± 0.6) × 10 9 M −1 s −1, respectively. The activation energies that are recommended for k 1 and k 2 are taken from Erickson et al. (1977) as 46.0 kJ mol −1 and 43.9 kJ mol −1, respectively. The reaction proceeds via three independent pathways that involve a nucleophilic attack on ozone by SO 2− 3, HO-SO − 2, and SO 2·H 2O. Rate laws and kinetic data of five investigators are compared for an open cloud water system with a liquid water content of 0.2 g m −3.