The presence of magnesium in glasses of geological, medical, and technological interests influences their physicochemical and durability properties. However, the understanding of the role of magnesium is dependent on the combined knowledge of the structural environment of magnesium in the glass or melt and of the silicate network connectivity of the studied systems. In this article, we present a Raman spectroscopic study of the network connectivity of 10 ternary silicate glasses in the system Na2OMgOSiO2 and one Mg-free binary silicate glass Na2OSiO2. Results obtained at constant polymerization suggest the existence of various Qn units according to the nature of the modifying cation. As polymerization decreases for Na2OMgOαSiO2 glasses (labeled as NMSα with α decreasing from 10 to 2), the band associated with SiOSi bending in fully polymerized region disappears being gradually replaced by a band attributed to SiOSi bending in region containing mainly Q2 and Q3 species. For highly polymerized glasses (NMS10-NMS4), the coexistence of these two bands suggests the presence of two interconnected networks. Concomitantly, the signal associated with Q3 species first increases. For a further decrease of the polymerization, the high wavenumber part of the signal associated with Q3 species decreases, while the intensity of the high wavenumber part of the band related to Q2 species increases. This result strongly suggests that magnesium charge-balances preferentially Q2 species rather than Q3 species. Copyright © 2010 John Wiley & Sons, Ltd.