Thermodynamic properties of Li3N dissolved in the molten LiCl salt at 900 K were explored using electrochemical methods. It was difficult to determine precisely the decomposition voltage of Li3N dissolved in the molten salt by cyclic voltammetry. The oxidation wave of N3- ion could not be located with high accuracy. However, the lithium activity of the Pb-Li alloy in equilibrium with the molten salt containing dissolved Li3N under nitrogen atmosphere could be measured electrochemically with high accuracy using the Li/Li+ reference electrode. Under the conditions used in this study, the potential of the Li-Pb electrode is equal to the decomposition voltage of Li3N. The activity of Li3N in molten LiCl was determined for anionic fractions of N3- ranging from x(N3-) = 10(-4) to 0.028. The nitride ion concentration in the salt was determined by chemical titration. The activity coefficient of the Li3N at high dilution was found to be very low, around 10(-4). The activity coefficient increases sharply with composition and has a value of 0.25 at x(N3-) = 0.028.