Li2S-SiS2-Li3N fast lithium ion conducting glasses were prepared by a melt-quenching procedure for the compositions (60 - 3x/2)Li2S . 40SiS(2). xLi(3)N (X = 0, 3, 5). Both temperatures of glass transition and crystallization increased with an increase in the Li3N content. The temperature dependence of conductivities followed an Arrhenius type equation. The incorporation of nitrogen into the glasses increased the conductivities at room temperature and decreased the activation energies for conduction. The lithium ion transport number of the thionitride glasses was more than 0.999. The glasses were electrochemically stable, exhibiting a very wide electrochemical window of about 10 V.