Binary metal alloy nanoparticles (AgNi, CuNi, AgCu, NiSn, NiSb) were prepared by injection of an oleylamine solution of metal precursors to a mixture of oleylamine and octadecene at 230 °C. Dynamic Light Scattering (DLS), Transmission Electron Microscopy (TEM), Elemental analyses (ICP OES), and Small-Angle X-ray Scattering (SAXS) analyses were performed for determination of the chemical composition, average size, size distribution, and shape of the prepared nanoparticles. Plasmon resonances were also observed. Phase separation was followed by High Temperature X-Ray Diffraction (HT-XRD) technique and was confirmed by Scanning Electron Microscope (SEM) and by measuring of magnetic properties during heating. The CALPHAD method was used for modelling of size-dependent phase diagrams of binary systems. Temperatures of invariant reactions were obtained by DSC measurements and experimental results were compared to calculated values.