One of the problems in marketing the wood of Prosopis and Acacia is the lack of standardization of its qualities. The aim of this paper was to obtain a preliminary detection of some properties of the wood of four species of the genus Prosopis and one species from Acacia grown in Argentina. To accomplish this objective, the content of extractives and some physical and mechanical characteristics were analyzed. The density rho(12) of all the species indicates that these woods range from heavy to very heavy (>or=0.69g/cm(3)). The total volumetric shrinkage values are low, less than 10%, for all species. The parallel compression strength and the shear strength for all the species indicate a very resistant wood (>or=46.93MPa and >or=18.35MPa, respectively). Brinell hardness was higher than 5kg/mm(2) in all cases. The species with less content of extractives is P. ruscifolia (approximately 9% of anhydrous mass) whereas A. aroma was the one with the greatest content (approximately 25% of anhydrous mass in the heartwood).