Various 0.45 cm2 dye-sensitized solar cell (DSSC) devices of glass/FTO/blocking layer/TiO2/dye/electrolyte/nano-thick Pt/glass structure were prepared by varying the Pt layer thickness from 10 to 100 nm. The phase and roughness of Pt layers were examined using XRD and AFM measurements. The catalytic activity of Pt was checked by cyclic voltammetry. The sheet resistance and interface resistance of Pt were examined using four point probe and impedance measurements. The reflectance of Pt was measured by uv-vis-nir spectroscopy. The photovoltaic energy conversion efficiency (ECE) was checked using a solar simulator and potentiostat. The XRD and AFM showed that crystalline Pt layers were formed with even surface roughness in nano thicknesses. The catalytic activity and conductivity of Pt increased with increasing thickness. The UV-Vis-NIR result revealed that the average reflectance decreased drastically as Pt layer thickness decreased less than 30 nm. The ECEs of DSSCs showed as 4.11% and 6.57% with thicknesses of 10 nm and 100 nm. The ECEs of DSSCs showed the same above 30 nm. Our results implied that a Pt thickness of larger than 30 nm might offer appropriate ECE.