Interaction of two different samples of graphene with DNA nucleobases and nucleosides is investigated by isothermal titration calorimetry. The relative interaction energies of the nucleobases decrease in the order guanine (G)>adenine (A)>cytosine (C)>thymine (T) in aqueous solutions, although the positions of C and T seem to be interchangeable. The same trend is found with the nucleosides. Interaction energies of the A–T and G–C pairs are somewhere between those of the constituent bases. Theoretical calculations including van der Waals interaction and solvation energies give the trend G>A∼T>C. The magnitudes of the interaction energies of the nucleobases with graphene are similar to those found with single-walled carbon nanotubes.