The thermal behavior of 1,3-propanediammonium (Pda) polyvanadates: [PdaH(2)](VO3)(2) (1), [PdaH(2)](3)V10O28. 5H(2)O (2), [PdaH(2)](2)H2V10O28 (3), and 1,6-hexanediammmonium (Hda) polyvanadates: [HdaH(2)](VO3)(2) (4), [HdaH(2)](3)V10O28. 2H(2)O (5), [HdaH(2)](2)H2V10O28. 2H(2)O (6) was studied in air atmosphere. The thermal decomposition of polyvanadates is a more-steps process consisting of simultaneous processes involving also vanadium. V2O5 is the final decomposition product formed from all polyvanadates studied. The new compounds, hexanediammonium decavanadates 5 and 6 were prepared by the reaction V2O5 with 1,6-hexanediammine in aqueous solution. The IR spectra confirmed the presence of the decavanadate anion in these compounds.