Galactomannan extracted from seeds of Cassia grandis with 0.1 M NaCl, followed by ethanol precipitation, presented a yield of 36 ?? 8%. The polysaccharide has a constant mannose/galactose ratio (2.44:1). Methylation analysis, one and two dimensional NMR spectroscopy confirmed that the polysaccharide has a central core composed of 4-linked ??-mannose units, with branches of galactose, linked to the carbohydrate core through ??(1???6) linkage. The amorphous nature of the galactomannan was confirmed by X-ray diffraction. Rheological characterization exhibited Newtonian plateaus followed by shear-thinning zones characteristic of polymer solutions up to 1.5% (w/v) and above this value the system exhibited yield stress associated with a weak gel. Adjusting stress-strain curves confirmed a 1.6% (w/v) as the galactomannan concentration value for the sol???gel transition. These results indicate that the galactomannan extracted from C. grandis seeds presents rheological characteristics suitable for applications in pharmaceutical, biomedical, cosmetic and food industries.