Abstract: The dynamics of neutral diglycine collision with highly oriented pyrolytic graphite (HOPG) were studied by molecular dynamics simulations using a reactive force field. The simulations were performed at an initial incident energy of 481.5 kJ/mol for four different initial incident polar angles of 0°, 20°, 45°, and 70°, and a surface temperature of 677 K. The angular, translational and internal energy, and residence time distributions of the scattered products were determined and analyzed. As a polyatomic molecule, diglycine has several low frequency vibrational modes and shows a rather strong attraction to HOPG, which leads to a long residence time on the surface and facile energy loss, particularly along the normal surface. Since there is significant normal momentum lost while parallel momentum is partially conserved, the scattering angular distribution is found to be generally superspecular and the final translational energies are much lower than the values predicted by the so-called hard-cube model. This study extends our knowledge of collisional energy transfer during collisions of polypeptide molecules with HOPG, which is expected to help the design of a neutral-gas concentrator for the fly-by collection of such molecules in rarefied atmospheres.