Taiwan The compositional inhomogeneity of Pd70Ag30 nanoparticles is studied. The composition of the as-prepared Pd 70Ag30 nanoparticles by chemical reduction across the diameter is inhomogeneous due to different reduction potentials of Pd and Ag. During the heat treatment, Ag will migrate to the surface because of its lower surface energy. Surface modification can change the surface energy and composition during the oxidation and sintering processes. Surface modification of Pd70Ag30 nanoparticles by polyethylene glycol will decrease the surface energy of Ag and assist the diffusion of Ag from the core to the surface. This makes the nanoparticles easier to sinter together. Surface modification by stearic acid has the opposite effect and results in less sintering of the nanoparticles.