Steady-state N2O decomposition reaction on polycrystalline Pt and Rh surfaces has been studied using a supersonic free-jet molecular beam (2.1 x 10(18) molecules/cm(2) s). The energy of the incident N2O beam was controlled by a nozzle heating technique in conjunction with a seeding technique. The decomposition rate shows both translational and vibrational energy dependence on the Pt surface. However, there is also the surface temperature dependence of the decomposition rate even varying the incident beam energy, indicating precursor-mediated dissociation of N2O on the Pt surface. On the other hand, no energy dependence was observed on the Rh surface, suggesting that the decomposition dynamics are different between Pt and Rh surfaces.