Alloy nanoparticles of PdxNi100-x (x = 20, 30, 70, and 80) were prepared by the coprecipitation method. The surface segregation of nanoparticles, driven by the surface energy, strain energy, and reduction potential, was studied systematically. The surface composition, surface species, and alloy structure of as-prepared PdxNi100-x and heated Pd30Ni70 alloy nanoparticles was characterized by ESCA, TPR, and XRD, respectively. The structure of as-prepared PdxNi 100-x alloy nanoparticles is not homogeneous and changes with the alloy content x. The surface is Pd enriched for as-prepared Pd 80Ni20 alloy due to the strain energy effect. In contrast, the surface is Ni enriched for as-prepared PdxNi100-x alloy with x = 20, 30, and 70 due to the reduction potential effect. In addition, a combinatory process of surface segregation and homogenization during the heat treatment was observed on the surface of Pd30Ni 70 alloy nanoparticles after heating at T > 620 K.