Partial molar heat capacities (C⁰_p2) and volumes (V⁰₂) of some nucleic acid bases, nucleosides and nucleotides in 1, 3 and 6 mol kg^–1 aqueous urea solutions have been measured using a dynamic-flow microcalorimeter and a vibrating-tube digital densimeter, respectively. The corresponding heat capacity and volume transfer parameters from water to aqueous urea solutions have been used to understand the nature of interactions between the constituents of nucleic acids and urea molecules. It has been inferred that urea molecules have weaker interactions with the nucleic acid bases at low concentrations of urea. However, at high concentrations of urea, the significantly positive values of heat capacities (C⁰_{p2, tr}) and volumes of transfer (V⁰_{2, tr}) indicate stronger hydrophilic–hydrophilic/ionic group interactions of the nucleic acid bases, nucleosides and nucleotides with urea and which may be responsible for the denaturation of the nucleic acid helix in high concentration aqueous urea solutions.