The growth and assembly of TiO2 nanostructures with enhanced charge transfer and light harvesting have attracted much attention for fabricating highly efficient dye-sensitized solar cells. In this study, we report an environmentally friendly and easy synthetic route for fabrication of mesostructured anatase TiO2 by controlling the hydrolyzing of n-butyl titanate in boric acid solution. The well-defined mesoporous TiO2 aggregates are obtained by the tensorial reaction-limited aggregation probability. The photovoltaic measurements indicate that the mesoporous TiO2 layer enhances the dye loading capacity, the electron transfer efficiency, and the photocurrent of the cell, contributing to the significant improvement of the energy conversion efficiency of the dye-sensitized solar cells.