Silver-containing chalcogenide glasses are of considerable interest for applications in optical and electrical recordings and as solid electrolytes. Therefore, insight in their structural properties is important. A neutron thermodiffraction study of Ag x (Ge 0.25 Se 0.75 ) 100−x glasses with x=15 and 25at.% was carried out. The amorphous samples were heated in situ from room temperature up to 350°C, while the neutron diffraction spectra were collected every degree. For both glasses the Ag 8 GeSe 6 phase appeared first, followed by the crystallization of GeSe 2 . The crystallization process for the Ag-rich glass was more complex with the appearance of a non-identified third phase. Rietveld refinement helped us in studying the evolution of the lattice constants of each phase upon heating.