Congo red (CR) is a symmetrical azo dye that has been used extensively in histochemistry, as staining agent for amyloid proteins and a host of other pharmacological applications. However, recently is has been found to form aggregates in aqueous solution and, in addition to its ï°-ï° packing properties, makes Congo red useful as a supramolecule. Its thermodynamic properties that are pertinent in evaluation and accurate interpretation of its interaction with solvents and other solutes are also very important. These parameters such as partial molar volume, viscosity, density and index of refraction have been determined in this work. The partial molar volume and the refractive index of this compound were determined as 296.86 ï± 4.16 cm3/mol and 1.4118 ï± 0.0000, respectively. The rest of its physico-chemical properties were determined as a function of its concentrationwhich ranged from9.58 x 10-3 to 4.69ï´10-2M.