Mesoporous TiO2 thin films on ITO/PEN substrate were prepared from two substantially different sizes of TiO2 nanoparticles by low temperature heat treatment. Using these thin film electrodes, flexible dye-sensitized solar cells(DSSCs) were assembled and their photovoltaic characteristics were investigated. The cell of TiO2 film prepared from the larger nanoparticle of 16 nm showed, as expected, much better photoconversion effciency than that from the smaller nanoparticles of about 5 nm due to the increased porosity and surface area for the same amount of TiO2. However, the photocurrent for the former cell did not increase as much as the amount of the increased surface area compared with the latter cell, which means that the interconnectivity between the nanoparticles in the former cell became poorer than that of the latter cell. When TiO2 film was prepared by mixing the larger nanoparticles and the smaller ones in the ratio of 9:1, the prepared solar cell showed much better photoconversion efficiency than the cell with the larger particles only. This means that the smaller particles increased the interconnectivity between the larger particles by filling the void volume without decreasing the porosity and surface area of the TiO2 film.