Bi nanoparticles embedded in a SiO2 matrix were prepared via the high energy ball milling method.The melting behavior of Bi nanoparticles was studied by means of differential scanning calorimetry (DSC) and hightemperature in situ X-ray diffraction (XRD).DSC cannot distinguish the surface melting from ‘bulk’ melting of the Bi nanoparticles.The XRD intensity of the Bi nanoparticles decreases progressively during the in situ heating process.The variation in the normalized integrated XRD intensity versus temperature is related to the average grain size of Bi nanoparticles.Considering the effects of temperature on Debye-Waller factor and Lorentz-polarization factor,we discuss the XRD results in accordance with surface melting.Our results show that the in situ XRD technique is effective to explore the surface melting of nanoparticles.