Dissociation dynamics of Ar cluster ions, Ar-n(+) (n = 3 - 16), in collision with He and Ne atoms was investigated by measuring the absolute dissociation cross sections and the branching fractions of the product ions at the collision energies of 0.1-10 eV in the center-of-mass frame. The cross sections and the branching fractions were successfully explained in terms of collisional excitation of the parent cluster ion and subsequent dissociation of it; the collisional excitation was treated by a hard sphere collision model with the aid of the molecular dynamics (MD) and the diatomics-in-molecules (DIM) calculations reported previously, and the subsequent dissociation was explained by the Rice-Ramsperger-Kassel (RRK) theory.