A donor-acceptor type organic dye connected with a quinoidal thiophene as a π-conjugated chain, cyano-[5'-(4''-(N,N-dimethylamino)benzylidene)-5H-thiophen-2'-ylidene]acetic acid, was synthesized and applied to dye-sensitized solar cells (DSSCs). The absorption band of this quinoidal thiophene dye appeared at longer wavelengths than those of dyes with similar π-conjugation length, indicating the effective π-conjugation through the quinoidal structure. Although the excited state of the quinoidal thiophene dye is deactivated within several picoseconds even in solution, the DSSCs using the quinoidal thiophene dye showed incident photon to current conversion efficiency (IPCE) values of more than 90%, demonstrating the fast and efficient electron injection from the excited dye to TiO(2). By optimizing the fabrication conditions, the DSSC using this dye afforded a photoelectric conversion efficiency of 5.2%, without enlarging the molecular size.