With the help of the amount of the complex (a), the concentration of the solution (b), the heat effect of dissolution process (Q) and the molar enthalpy of dissolution in water (Δ_dissH) of M(NTO)_n·mH₂O (M=Ba, n=1, m=3; M=Li, n=1, m=2; M=Ca, n=2, m=4; M=Na, n=m=1; M=Co, Mg, n=2, m=8; M=Ce, Pr, Gd, n=3, m=7; M=Tb, Dy, n=3, m=5; M=Y, Yb, n=3, m=6; NTO=3-nitro-1, 2, 4-triazol-5-one) obtained by a Calvet microcalorimeter, five empirical formulae describing the differential enthalpy of dissolution(Δ_difH^θ_m), standard molar enthalpy of dissolution ［Δ_dissH^θ_m(b=0)］, relative apparent molar enthalpy (Δ_dissH_apparent), relative partial molar enthalpy (Δ_dissH_partial) and enthalpies of dilution (Δ_dilH_1,2) in water of these metal complexes of NTO were obtained.