The molecular structure of tetraselenafulvalene (TSeF) dissolved in a nematic crystal solvent is determined from the PMR spectra including 77Se satellites. The molecule is found to be either puckered in a boat form or possessing a broad potential function for the in-phase puckering motion. The dihedral angle between the SeHCCHSe and Se2CCSe2 plane is 15.5 ± 0.6°. The structure is in good agreement with that of the dimerized TSeF in the solid state. Some 77Se indirect coupling constants are also determined. © 1980, All rights reserved.