Neutron and X-ray diffraction measurements were performed to investigate the structure of Na2S-GeS2 glasses synthesized by mechanical alloying. The Ge-S coordination numbers calculated from the total correlation functions show that GeS4 tetrahedra form the basic framework structure of Na2S-GeS2 glasses. In addition, a three-dimensional structural model of the (Na2S)(50)(GeS2)(50) glass was obtained by using reverse Monte Carlo (RMC) simulation on neutron and X-ray diffraction data, and it was compared with the RMC model previously obtained for a (Li2S)(50)(GeS2)(50) glass. The results show that the Ge-S framework structures in the two glasses are almost the same in the short and intermediate ranges; that is, the Ge-S framework structures are formed mainly by the connection of corner-sharing GeS4 tetrahedra. Many of the Na ions are coordinated by four S atoms, which are non-bridging S atoms and/or bridging S atoms. (C) 2009 Elsevier B.V. All rights reserved.