Physico-chemical and rheological characterization of the gum extracted from the endosperm of vinal (Prosopis ruscifolia) seeds was performed. The CG-MS analysis revealed that vinal gum is a galactomannan with a mannose/galactose ratio of 1.6, with traces of arabinose and glucose residues. The structure was further confirmed by 13C NMR which showed several similarities between vinal gum and guar gum spectra. The viscosity molecular weight was 1.43 ± 0.04·106 Da (obtained from Huggins plot) and the average number molecular weight was 0.7·105 Da. Shear continuous rheology studies showed a shear thinning behavior at concentrations higher than 0.04% (w/v) of vinal gum and an apparent viscosity slightly lower than that of guar gum at the same concentration. Mechanical spectra revealed that vinal gum has a typical macromolecular solution behavior with the moduli crossing point that characterized semi-diluted (0.16–0.3% w/v) gum solutions. The present work provides structural, physicochemical and rheological information of a new galactomannan from an abundant and available non-traditional source, being a starting point for food, pharmaceutical or other industrial potential applications of vinal gum.