Single crystals of Rb2H2P2O6·2H2O could be obtained from aqueous solutions of hypodiphosphoric acid and rubidium carbonate. Its crystal structure was determined by X-ray diffraction and it crystallizes in the monoclinic space group P21/c with Z = 4. The salt-like title compound consists of [H2P2O6]2– units in staggered P2O6-skeleton conformation, Rb+ cations, and H2O molecules, held together by intermolecular hydrogen bonds of the type O···O. The vibrational spectra (IR/FIR and Raman) of the rubidium salt were recorded and an assignment of the vibrational modes is proposed based on the point group C2h for the P2O6-skeleton of the anion. The thermal behavior of Rb2H2P2O6·2H2O is dominated by a complex TG decay indicating a simultaneous H2O delivery coupled with a disproportionation of [H2P2O6]2–, what is also supported by Raman spectra of heated samples.