Geometries and stabilities of the linear aluminum-bearing carbon chains AlC 2 n H (n=1–5) in their ground states have been explored by the DFT-B3LYP and RCCSD(T) methods. Structures of the X 1 Σ + and 1 1 Π electronic states have also been optimized by the CASSCF approach. The studies indicate that these species have single–triple bond alternate pattern, AlCCCC⋯CCH, and the electronic excitation from X 1 Σ + to 1 1 Π leads to the shortening of the AlC bonds. The vertical excitation energies of the 1 1 Π←X 1 Σ + and 2 1 Π←X 1 Σ + transitions for AlC 2 n H (n=1–5) have been investigated by the CASPT2, EOM-CCSD, and TD-B3LYP levels of theory with the cc-pVTZ basis set, respectively. CASPT2-predicted 1 1 Π←X 1 Σ + transition energies are 3.57, 3.44, 3.33, 3.26, and 3.21 eV, respectively. For AlC 2 H, our estimate agrees very well with the experimental value of 3.57eV. In addition, the AlC bond dissociation energies and the exponential-decay curves for these vertical excitation energies are also discussed.