A pi -conjugated polymer containing a dithiafulvene unit and a bipyridyl unit was prepared by cycloaddition polymerization of aldothioketene derived from 5,5'-diethynyl-2,2'-bipyridine. Utraviolet-visible (UV-vis) absorption spectra showed that the pi -conjugation system of the polymer expanded more effectively than that of a benzene analogue of poly(dithiafulvene) obtained from 1,4-diethynylbenzene. Cyclic voltammetry measurements indicated that the dithiafulvene-bipyridyl polymer was a weaker electron-donor polymer than the benzene analogue. These results supported the idea that the incorporation of the electron-accepting bipyridyl moiety into conjugated poly(dithiafulvene) induced an intramolecular charge-transfer (CT) effect between the units. Treatment of the dithiafulvene-bipyridyl polymer with bis(2,2'-bipyridyl)dichlororuthenium. (II) [Ru(bpy)(2)Cl-2] afforded a ruthenium-polymer complex. A cyclic voltammogram. of the complex showed broad redox peaks, which indicated electronic interaction between the dithiafulvene and tris(bipyridyl) ruthenium complex. The dithiafulvene-bipyridyl polymer formed CT complexes with 7,7,8,8-tetracycanoquinodimethane (TCNQ) in dimethyl sulfoxide. The UV-vis. absorption indicated that the resulting CT complex contained anion radical of TCNQ and partially charge-transferred TCNQ. The polymer showed an unusually high electrical conductivity of 3.1 x 10(-4) S/cm. in its nondoped state due to the effective donor-acceptor interaction between the bipyridine unit and the dithiafulvene unit.