Barium–sodium borosilicate  glasses containing upto 6 wt% fluoride ions were prepared by conventional melt quench method and characterized by ¹⁹F, ²⁹Si and ¹¹B nuclear magnetic resonance (NMR) techniques. ¹⁹F NMR studies have confirmed the presence of mainly linkages like F–Si(n) or F–B(n) along with F^–Ba(n). Their relative concentrations are unaffected by F^- content in the glass. Incorporation of fluoride ions in the glass is associated with significant reduction in the nonbridging oxygen concentration attached to silicon, as revealed by the increase in the concentration of Q³ structural units of silicon at the expense of Q² structural units. ¹¹B NMR studies have established that the relative concentrations of BO₃ structural units are higher for F^- ion containing glasses compared to the one without F^- ion incorporation. The observed increase in the relative concentrations of Q³ structural units of silicon and BO₃ structural units with fluoride ion incorporation in the glass has been attributed to the formation of F^–Ba(n) type of linkages, thereby reducing the concentration of network modifying cations for breaking the Si–O–Si/B–O–B linkages. Formation of such structural units weakens the glass network thereby decreasing the glass transition temperatures.