The kinetic study of naphthalene (N) ozonation in aqueous solution was carried out in order to specify the pathway of the initial ozonation step of this compound. Indeed, according to the data presented in part I (ozone consumption and ozonation products) three reactional pathways can be considered: an electrophilic substitution of ozone on carbon 1 (or 2) of the naphthalene, two simultaneous 1,3-dipolar cycloadditions of ozone on 1,2 bond and on 3,4 bond of naphthalene, one 1,3-dipolar cycloaddition of ozone on 1,2 bond of naphthalene. This kinetic study was carried out mainly at pH 5.6 at 1°C in a batch reactor (Fig. 1). The initial concentrations of reactants were chosen so that the opening of a second aromatic ring of naphthalene would not be significant. [ naphthalene]0 = 0.449.7 10− 5 mol] −1 [ ozone] 0 = 0.6-1.1 10− 5 mol] −1 All the results (Figs 2 and 3; Table 1) obtained at pH 5.6, by analysis of ozone and naphthalene consumed showed that: the stoichiometry of the initial reaction step was 2 mol of ozone by mol of naphthalene, a two-order kinetic law: − d N = k N [O 3][N] was verified for a large period of time and with different initial concentrations (linear correlation about 0.99), the average of rate constant values (1°C, pH 5.6) was 550 ± 801 mol −1 s −1. These data exclude on the one hand the hypothesis of an electrophilic substitution which requires a stoichiometry at least equal to three, and on the other the hypothesis of two simultaneous 1,3-dipolar cycloadditions which implies a three-order kinetic reaction. The same experiments carried out at pH 4.3 and 6.8 (Table 2) showed a low increase of k N between pH 4.3 and 5.6. However, k N increased in fact at pH 6.8. This phenomenon is probably the consequence of the decomposition of ozone in water at neutral pH. The kinetic study made at different temperatures (Fig. 5) allowed us to determine the value of the activation energy ( E a ⋍ 8 kcal mol −1 at pH 5.6 ). So, the value of the rate constant at 20°C and pH 5.6 ( k N ⋍ 1500 l mol −1 s −1 ) is practically the same as the value mentioned by Hoigne when the reaction is carried out at 20°C with pH 2 in presence of radical scavengers. Finally, the rate constant values of 1-chloro naphthalene and 2-methyl naphthalene, given in Table 3, allowed us to predict that the initial attack of ozone on 1,2 bond of naphthalene is of an electrophilic nature.