The FT-infrared (IR) and Raman spectra of the radical anion of α,ω-diphenyl-1,3,5,7,9-decapentaene (DP 1 0 - ), a polyene molecule with five conjugated C C bonds, were observed in vacuum condition. The IR absorption spectrum for ionic species of polyene molecule was observed for the first time in the experimental method. The C C stretching band of IR absorption has the weak at 1591-1603cm - 1 , while the Raman band has the two intense peaks at 1533 and 1574cm - 1 . In IR absorption, the in-plane CH bending has the several strong bands between 1448 and 1551cm - 1 , whereas the Raman has a strong band used as a marker of negatively charged polyene at 1272cm - 1 . The origin of IR and Raman spectra of DP 1 0 - is discussed in terms of a polaron model compound in polyacetylene.