To improve performance of dye-sensitized solar cell(DSSC), thermally reduced graphene oxide(rGO) was investigated as Pt-free counter electrodes(CE) material. The DSSCs with rGO were fabrcated by simple spin coating method under different temperature and ambient atmospheres like Ar, N-2 and air. When the rGO CE was reduced at 450 degrees C under the Ar atmosphere, it was obtained the power conversion efficiency of 6.02%, which showed the high catalytic activity and performance of DSSC as much as Pt. This value means the thermally reduced rGO CEs under the Ar gas will be suitable as a substitute for Pt CEs.