Density functional theory calculations are presented for the linear cyanopolyacetylenes H(C ≡ C) n C ≡ N, dicyanopolyacetylenes N ≡ CC 2 n - 2 C ≡ N (n = 1-3), and their geometrical isomers. The structures, vibrational frequencies and dipole moments are computed by BLYP and B3LYP theory with the 6-311G* and 6-311G** basis sets. Good agreements are observed between the computed properties of the ground state of these molecules and experimental observations.