B3LYP/LanL2dz density functional theory calculations have been carried out on structure and stability of (GaP)_n and (GaP)_n^－ (n＝10～16) clusters. It is focused on the changes in structural and electronic properties upon the addition of an electron to the corre-sponding neutral clusters. Harmonic vibrational frequency analysis presented predicts that the strongest in-frared vibrational mode is in the 341～390 cm^－1 regions. Among different (GaP)_n and (GaP)_n^－ (n＝10～16) clusters, (GaP)₁₂ and (GaP)₁₂^－ with T_h symmetry are the most stable in consideration of energy gap, binding energy and energy secondary differences. At the same time, (GaP)₁₆ with T_d symmetry is also more stable than other species. It should be observed by experiments, which of clusters on earth is the most stable. And the vertical detach-ment energies (VDEs) of (GaP)_n^－ and the adiabatic electron affinities (AEAs) of (GaP)_n were calculated, which should be useful for the analysis of future data.

Key words: density functional theory, (GaP)_n and (GaP)_n^－ clusters, vertical detachment energy, adiabatic electron affinity