Graphite was found to be a superior support for Pd catalyst for the direct synthesis of H2O2 from H-2 and O-2. The Pd/graphite catalyst prepared by HCHO reduction showed much higher H2O2 formation activity and selectivity than that prepared by impregnation. The size and morphology of Pd nanoparticles may play roles in H2O2 formation. The worm-like small Pd nanoparticles over graphite surfaces exhibited higher catalytic performances in H2O2 formation.