Three modes of synchronous ozone addition ([6.6]-, [5.6]-, and 1,4-addition) to C(60) fullerene and three modes of ozone addition to C(70) (ab-, cc-, and de-addition) have been studied using density functional theory calculations. Comparison of activation enthalpies shows that in the case of C(60), [6.6]-addition of ozone is the most favorable energetically and occurs without a barrier. In the case of the C(70) fullerene, additions to ab- and cc-bonds are the most favorable. The initial step of interaction between a C(60)/C(70) and O(3) is the formation of a molecular complex, which then converts into a primary ozonide. The calculated rate constant of the [6.6]-addition to the C(60) fullerene according to the proposed scheme is 3.90 x 10(6)L mol(-1)s(-1), which corresponds well to the experimental value.