The kinetics of oxidation with ozone of 1,3,6-naphthalenetrisulfonic acid was analysed by studying the influence of different experimental parameters such as the concentration of tert-butyl alcohol (2-methyl-2-propanol), initial concentration of the acid, pH, and temperature. The rate constant of the direct reaction at 25degreesC was calculated (k(D) = 6.72 m(-1)s(-1)). The constant of the free radical reaction was determined with the competitive kinetics method, using sodium 4-chlorobenzoate as reference compound, obtaining a value of k(OH) = 3.7 x 10(9)m(-1)s(-1). It was demonstrated that even at very acid pH values, 80% of the 1,3,6-naphthalenetrisulfonic acid was degraded by free radical reactions, so that the ozonation of this acid may be considered an advanced oxidation process.