The dynamics of electron-transfer processes between bis(tetrabutylammonium) cis-bis(thiocyanato)bis(2,2'-bipiridine-4,4'-dicarboxylato)ruthenium(II) (called N719) and nanostructured ZnO films were studied by femtosecond and nanosecond spectroscopy. The incident photon to current conversion efficiency (IPCE) for these dye-sensitized electrodes was 36% in the max. of 530 nm, corresponding to a quantum efficiency of 80%. The highest IPCE values were obtained when the electrodes were prepd. under conditions where formation of dye aggregates in the pores of the nanostructured films is avoided. For such films, the electron injection time was in the subpicosecond regime (<300 fs), which is comparable to the N719-TiO2 system. The back electron-transfer kinetics between conduction band electrons and oxidized dye mols. were biexponential with time consts. of 300 ns and 2.6 μs. Variation of the light intensity did not affect the time consts., but only their relative wts. The kinetics of back electron transfer in the N719-ZnO and N719-TiO2 systems are identical.