The conformations and vibrations of 1,2-dimethoxyethane (DME) have been studied by density functional theory (DFT) in comparison with the molecular orbital (MO) methods. The calculations using the 6-31G* basis set were performed by five DFT methods (BVWN, BP86, BLYP, B3PW91, and B3LYP) and two MO methods (HF and MP2). The energies of conformers were better predicted by the DFT methods using the B3 exchange functional than other methods. The vibrational wavenumbers calculated by the DFT and MO methods explained, after correcting with uniform scaling, the observed Raman and infrared spectra of the normal and perdeuterated species of DME. It was confirmed that the conformer of DME present in the solid state is TGT, and the conformers in the liquid state are TGT, TTT, TGG＇, and TTG. The present calculations further indicated that the TGG and GGG conformers are also present in the liquid state. The distributions of the ratio of the unsealed calculated wavenumber to the experimental wavenumber are narrower with the B3PW91 and B3LYP methods than with other methods, indicating that these two methods, when making appropriate uniform scaling corrections, give wavenumbers in excellent agreement with the experimental wavenumbers. In conclusion, the performance of the B3PW91 and B3LYP methods is the best among the DFT and MO methods used in this work in reproducing the experimental results of the energies, molecular geometries, and vibrational wavenumbers for DME.