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We have studied the optical absorption properties of CdS quantum dots (QDs) adsorbed on TiO2 electrodes and the photovoltaic properties of CdS quantum dot-sensitized solar cells (QDSSCs). CdS QDs were grown directly on a nanostructured TiO2 surface by a chemical bath deposition method for different adsorption times from 30 min to 8 h. The growing size of CdS QDs on the TiO2 electrodes with increasing adsorption time was confirmed by a redshift in the optical spectra, measured using photoacoustic (PA) spectroscopy. The steepness factor, which reflects the amount of disorder and the number of defects, was also estimated from the PA spectrum. The steepness factor decreased sharply at 1 h adsorption time when the CdS QDs commenced aggregating. Subsequently, the steepness factor increased for longer adsorption times, indicating that the density of surface states of the CdS QDs had decreased due to a decrease in the ratio of surface area to volume with the growth in average size. The photovoltaic properties of sandwich structure solar cells were studied under an illumination of air mass (AM) 1.5 using Cu2S on brass as a counter electrode and a polysulfide (S/S2−) redox system as the electrolyte. The maximum photovoltaic conversion efficiency obtained was 1.22%, which was for the device that had 2 h CdS adsorption. The variations in series resistance and shunt resistance were estimated from the slopes of photocurrent density-photovoltage curves near the short circuit and open circuit conditions, respectively. With increasing adsorption time, both resistances decreased until 2 h adsorption when the maximum photoconversion efficiency was observed. These results indicate that the CdS adsorption time is closely correlated with the photovoltaic properties of CdS QDSSCs.