To determine the exchange coupling constants between spins, magnon dispersion relation in FePt alloy was studied by neutron inelastic scattering measurements. Data analysis based on the localized spin model led to the result that magnetic moments of Pt atoms couple with those of Fe atoms anti-parallel. Powder diffraction measurements were also performed to determine the sizes and the direction of magnetic moments of Fe and Pt atoms. The results were 1.93 and -0.49 mu(B) for Fe and Pt, respectively. The results are consistent with those of magnon dispersion relation. (c) 2006 Elsevier B.V. All rights reserved.