We investigated effects of valeric acid (VA) as a co-adsorbate on the photovoltaic performance of dye-sensitized solar cells (DSSCs). When the introduction of VA onto TiO(2)surface was performed after dye (N719) adsorption, the DSSC with VA showed an increase in short-circuit current (J(sc)), open-circuit voltage (V-oc) and fill factor, resulting in a power conversion efficiency of 7.27%, compared to that (6.20%) of reference device without VA. Incorporation of VA on free TiO2 surface induced longer lifetime of electrons injected from excited dyes to conduction band of TiO2, leading to the increase of electron collection efficiency and the suppression of charge recombination between injected electrons and I-3(-) ions, and thus larger J(sc) and V-oc, respectively.