[Y(NTO)(2) NO3(H2O)(5)]. 2H(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 yttrium oxide. The single crystal structure has been determined by a four-circle X-ray diffractometer. The crystal is monoclinic, space group Cm with crystal parameters of a=0.6773(2) nm, b=2.0866(2) nm, c=0.6551(1) nm, beta=102.98(2)degrees, V=0.9021(1) nm, Z=2, D-c=1.970 g cm(-3), mu=33.487 cm(-1), F(000)=540. The final R is 0.032. Based on the thermal analysis, the thermal decomposition process of [Y(NTO)(2) NO3(H2O)(5)]. 2H(2)O has been derived.