The primary characteristic of nanopowders is the high surface area and consequently high fraction of atoms on the interfaces, which changes the energy of the system. The additive distribution in the nanopowder interfaces is a fundamental aspect to control the energy, particle size, and final properties of nanopowders. In this work, the surface excess was determined using a selective lixiviation method, where a low-water-soluble oxide, SnO2, was used as the matrix, and a high-water-soluble oxide, ZnO, was used as the additive. The X-ray photoelectron spectroscopy (XPS) analysis confirmed that ZnO segregated on SnO2 surfaces. However, after acid lixiviation the same analysis showed an undetectable surface concentration of ZnO. The evaluation of the nanostructure change and surface composition enables us to calculate the heat of segregation for the grain boundary (=-47.2kJ.mol-1) and surface (Hsegs=-36.4kJ.mol-1) and the interface energy reduction because of segregation. At low-ZnO concentrations, the additive solubilizes in the bulk and promotes particle growth. However, the segregation to the grain boundary and surface determines the relative stability of each interface, which promotes hard agglomeration and particle size stabilization at intermediated ZnO amounts. At high-ZnO concentrations, the surface segregation stabilizes the solid-gas interface and decreases the agglomeration and final particle size.