The average charges of fragment ions were theoretically studied for 1 MeV/atom C-n(+)(n=1-10) cluster ions penetrating carbon and aluminum foils. Here the clusters are assumed to be in linear-chain structures, and to have a random orientation and to be exploded via coulomb repulsion in a foil. The elastic scattering effect is included, where the screening length in repulsive interaction was proposed. The slowing-down of fragment ions in a solid was taken into account. The calculated results were in good agreement with the recent data. (C) 2006 Elsevier B.V. All rights reserved.