Conformational characteristics of poly(tetramethylene oxide) (PTMO) have been investigated on the basis of the conformational energies evaluated for its monomer model 1,4-dimethoxybutane (DMB) from the ab initio molecular orbital (MO) calculations at the second-order Moller-Plesset correlation level with the 6-31+G* basis set. The reliability of our conformational energies was examined by comparison between calculations and observations of NMR vicinal C-13-H-1 and H-1-H-1 coupling constants of DMB and the characteristic ratio and dipole moment ratio of PTMO. Then the C-O bond dipole moment (m(c-o)) for the rotational isomeric state analysis of polyethers was determined from the MO and H-1 NMR data reported previously for 1,2-dimethoxypropane, a monomeric model compound of poly(propylene oxide). The optimal m(c-o) value was obtained as 1.18 D. The conformational energies reproduced the experimental observations very well. The relationship between the conformational characteristics and crystal structures of polyethers [-(CH2)(y)-O-](x) (y greater than or equal to 4) is also discussed.