In this work, the power conversion efficiency (PEC) of dye-sensitized solar cells has been improved by using cosensitized nanocomposite photoanodes. In the first step, mix dye solutions of ruthenizer (N719) and organic dye (RK-1) have been prepared for the sensitization of pristine TiO2 films. Among these dye solutions, 0.2 mM N719/0.3 mM RK-1 solution gives the highest PCE of 8.45%, which is superior to that of individually sensitized solar cells (N719 = 6.54% and RK-1 = 5.69%). In the second step, nanocomposites of TiO2 and graphene have been prepared by changing the composition of graphene from 0.05% to 0.2%. The dispersion of graphene in TiO2 has been confirmed by transmission electron microscopy (TEM). The optimized dye solution of 0.2 mM N719/0.3 mM RK-1 has been used to sensitize TiO2/graphene thin films. The solar cell based on TiO2/0.1%GR nanocomposite film shows the power conversion efficiency of 9.45%, which is about 45% and 66% higher than TiO2/N719 and TiO2/RK-1 based DSSCs, respectively. The overall enhancement in PCE can be credited to increase light absorption, improve light harvesting efficiency and fast electron transport, which ultimately enhance the current density of solar cells.