The structures of aniline dimer cation are investigated by the density functional theory calculations at the B3LYP/ccpVDZ level. We obtained two stable conformational isomers which have 'NH... N'or'NH... pi' hydrogen bond. The NH... N isomer is more stable by 2.50 kcal mol(-1). The calculated infrared spectra suggest that the NH stretching vibrations due to the two isomers are overlapped in the experimental spectrum [Chem. Phys. Lett. 323 (2000) 43].