Spectral sensitization of nanocrystalline ZnO films has been carried out with ruthenium complex, bis-(2,2’-bipyridine)(2,2’-bipyridine-4,4’-dicarboxylic acid) ruthenium(II) or (Ru(II)). An incident photon to current conversion efficiency (IPCE) of 14% has been obtained for unbiased ZnO/Ru(II) photoelectrochemical cells. This low IPCE has been attributed to the poor light harvesting efficiency(LHE) and charge collection (eta(e)) efficiency. The weak interaction between Ru(II) and ZnO surface which results in poor uptake of Ru(II) on ZnO is responsible for a lower LHE while various charge recombination processes are the cause of poor eta(e). To better understand the process of photosensitization of ZnO by Ru(II), the dependence of IPCE and fluorescence on applied bias, and other photoelectrochemical measurements have also been carried out.