The effects of the nitric acid (HNO 3 ) treatment of TiO 2 nanoparticles on the photovoltaic properties of the dye-sensitized solar cell (DSSC) were investigated. The HNO 3 treatment enhanced the dispersion of TiO 2 particles, increased the surface area and porosity of the sintered TiO 2 films, increased the relative proportion of the Ti 3+ state in the Ti 2p X-ray photoelectron spectroscopy spectrum, significantly increased the amount of adsorbed dye molecules on the TiO 2 electrode, and reduced the charge-transfer resistance at the TiO 2 /dye/electrolyte interface. The short circuit photocurrent density (I sc ) was increased due to the increased amount of adsorbed dye molecules and the reduced charge-transfer resistance. The HNO 3 pre-treatment of TiO 2 particles improved the overall conversion efficiency of the DSSC by about 14%.