Department of Chemistry, Himachal Pradesh University, Summer Hill, Shimla-171 005, India Manuscript received 17 August 2004, revised 10 March 2005, accepted 29 March 2005 Partial molar volumes of oxalic acid and its salts viz. ammonium oxalate, sodium oxalate and potassium oxalate in water have been determined from solution density measurements at various temperatures and solute concentrations. The data have been evaluated by using Masson equation and the obtained parameters have been interpreted in terms of solute-solute and solute-solvent interactions. Structure making/breaking capacities of oxalic acid and its salts have been inferred from the sign of [ð2ᶲ0v/ðT2]P, i.e. second derivative of partial molar volume with respect to temperature at constant pressure. The oxalic acid and its salts act as structure breakers in water.