[Dy(NTO)(2)(H2O)6]. NTO . 4H(2)O was prepared by mixing the aqueous solution of lithium 3-nitro-1,2,4-triazol-5-onate and the dilute nitric acid solution of dysprosium oxide. The single crystal structure has been determined by a four-circle x-ray diffractometer. The crystal is monoclinic, space group P2(1)/n with crystal parameters of a=1.0094(1) nm, b=1.2586(2) nm, c=1.8845(2) nm, beta=106.31(1)(0), V=2.2978 nm(3), Z=4, mu=33.890 cm(-1), F(000)=1444, D-x=2.11 g cm(-3), lambda(MoKalpha)=0.071073 nm. The final R is 0.041. Based on the thermal analysis, the thermal decomposition mechanism of [Dy(NTO)(2)(H2O)6]. NTO . 4H(2)O has been derived. From measurements of the enthalpy of solution in water of [Dy(NTO)2(H2O)6]. NTO . 4H(2)O at 298.15 K, the standard enthalpy of formation, lattice energy, lattice enthalpy and standard enthalpy of dehydration have been determined as-(3894.5+/-6.5), -4525, -4560 and 306.9 kJ mol(-1), respectively.