In the present work, the behavior of crystals derived from two different crystallization methods applied in a concentrated aqueous lithium salt solution was studied. The LiOH·H2O crystals obtained by a simple evaporation (Crystal I) differed in terms of morphology and solubility from those precipitated from lithium hydroxide solutions by addition of ethanol as a co-solvent (Crystal II). Solubility of Crystal II at different temperatures (15 to 35°C) and mass ratios of ethanol to water (0 to 0.1) was determined. Polymorphic like behavior of these crystals was evidenced from X-ray diffraction patterns. Measurement of density, refractive index, absolute viscosity and electrical conductivity of saturated solutions are reported. A thermodynamic analysis in terms of the Chen model for the calculation of activity coefficients, indicate that the polymorphic system in water and in water + ethanol (ethanol/water ratio 0.1 ) is enantiotropic.