Surface formation markedly influences the stability and properties of nanoalloys. The surface states of nanoalloys are sensitive to the constituent elements and to the surrounding environment. In this study, Fourier transform-infrared (FT-IR) spectroscopy and an evolution strategy (ES) combined with density functional theory calculations and multivariate analysis were used to explore the stable configuration of NO-adsorbed PdRu nanoalloys. FT-IR analysis indicated that the NO molecules were adsorbed on the Ru-related sites, which was inconsistent with the stable surface state of the isolated PdRu nanoalloy models. The ES revealed that the stable surface state consisted mainly of Ru atoms owing to molecular adsorption. In addition, the Pd−Ru mixing was facilitated by the adsorption. According to the multivariate analysis, the adsorption energies on the Ru-related sites were more negative than those on the Pd-related sites and became more negative as the number of neighboring Pd atoms increased. These adsorption characteristics are opposite to those of the stability of the isolated PdRu nanoalloys. The energy gain owing to NO adsorption overcomes the energy loss due to the Pd−Ru bonds and placement of Ru atoms at the surface. This study highlights the importance of understanding stable surface states in a reactive atmosphere for the application of nanoalloys.