Abstract The local structures of Ag 3AsS 3 glass at 80 and 300 K have been investigated by extended X-ray absorption fine structure analysis. By comparing the glass structure with that of Ag 3AsS 3 crystal (proustite), the possibility of ionic conduction by this glass is discussed. The local structure around an As atom in the glass is similar to that in the crystal. This fact suggest that, even in the glass structure, the As atoms from AsS 3 trigonal pyramids of shape similar to that in the crystal. The AgS distance (2.449 Å at 300 K) and the large root mean square displacement, σ, for the AgS atomic pairs in the glass, groups with a by the parameter fitting method, show that the Ag atoms are quite randomly distributed around the AsS 3 groups with a similar AgS distance to that in the crystal. Further, it is possible that the large thermal contribution to σ AgS 2 for the glass may indicate the involvement of the Ag atoms in ionic conduction.