Precise vapor pressure data for LiCl and LiBr solutions in N,N-dimethylacetamide are given for T = (323.15 to 423.15) K. The molality ranges covered in this study are about m = (0.073 to 1.89) mol (.) kg(-1) for lithium chloride and in = (0.06 to 1.75) mol (.) kg(-1) for lithium bromide. Osmotic coefficients are calculated by taking into account the second virial coefficient of N,N-dimethylacetamide. The parameters of the extended Pitzer-ion interaction model of Archer, of the MSA-NRTL model and of the chemical model of Barthel are evaluated. These models accurately reproduce the experimental osmotic coefficients within different concentration ranges. The parameters of the Pitzer-ion interaction model of Archer are used to calculate the mean molal activity coefficients and excess Gibbs free energies. The non-ideal behaviors of these systems are discussed in terms of the model parameters. (c) 2004 Elsevier Ltd. All rights reserved.