We report the characterization of the interface formation of fullerene (C60) on hafnium (Hf) using x-ray and ultraviolet photoelectron spectroscopy (XPS and UPS). The valence band, C 1s and Hf 4f spectra were measured during the deposition of C60 on a clean Hf surface in a stepwise manner. After enough deposition of C60 layers on Hf, XPS measurements indicate that there is no chemical reaction between C60 on Hf, and band bending exists at the C60/Hf interface. From UPS measurements, the energy level difference between Fermi level of Hf and the onset of the highest occupied molecular orbital of C60 is 2.01 eV. The vacuum level of Hf was shifted toward low binding energy (0.95eV) as the C60 deposition. These valence spectra results indicate that there exist an interface dipole and small electron injection barrier at the C60/Hf interface. We provide the complete energy band diagram of the C60/Hf interface and confirm that a small electron injection barrier can be achieved by inserting a low work function metal in a C60 field-effect transistor.