Summary Recently, we have reported a noble method of preparing Ag/Rh bimetallic nanoparticles with a pseudo-core/shell structure. We simply mix the dispersions of poly(N-vinyl-2-pyrrolidone)(PVP)-protected Ag and Rh nanoparticles in solution at room temperature. We found that the mixture of dispersions forms bimetallic nanoparticles in a pseudo-core/shell structure on standing. We call this process the ‘self-assembling’ or ‘self-organizing’. In this study we seek for a thermodynamic driving force for this process by determining the enthalpy of the interaction among three pairs of nanoparticles by isothermal titration calorimetry (ITC). The results indicate that the interaction between each pair is strongly exothermic, and that among the pairs studied here the strength of the exothermic interaction is in the order of Ag/Pt<Ag/Pd<Ag/Rh.