The formation mechanisms of C-1(+), and C-2(+), and C-3(+) ions by laser ablation of graphite are investigated using time-of-flight (TOF) quadrupole mass spectroscopy. The laser ablation is performed in conjunction with a pulsed Ar expansion to elucidate the third-body effect on the formation of the small carbon cluster ions. Drastic enhancement of the C-2(+) ion signal is observed by an increase of the local pressure near the target, indicating that C-2(+) ions are efficiently formed by recombination of carbon atoms and subsequent ionization. The branching ratio of C-1(+), C-2(+), and C-3(+) ions and their mean translational energies are different from those of neutrals. Also, the TOF spectra for C-n(+) ions show multiple peak structures, which implies that different mechanisms are involved in the formation of C-n(+) ions.