Conformations of the ketyl radicals generated by metal reduction of 2-methyl-1, 1'-dinaphthyl ketone (I) and 1, 1'-dinaphthyl ketone (II) were evaluated on the basis of informations from electron spin resonance and visible absorption spectra, and molecular orbitals (MO) calculations. By comparing the experimental spin density and transition energies with the corresponding theoretical quantities obtained by McLachlan's method and by unrestricted PPP-SCF-MO method, the rotational angles about the C-C bond connecting the aromatic group were found to be about (0°, 60°) to (49°, 0°) for I and (34°, 34°) for II.