The enthalpy increments and the standard molar Gibbs energy of formation of NdFeO₃(s) have been measured using a high-temperature Calvet microcalorimeter and a solid oxide galvanic cell, respectively. A λ-type transition, related to magnetic order- disorder transformation (antiferromagnetic to paramagnetic), is apparent from the heat capacity data at & 687 K. Enthalpy increments, except in the vicinity of transition, can be represent-ed by a polynomial expression{H=(T)-H=(298.15 K)}/J'mol^-1(±0.7%)=- 53625.6+146.0(T/K)+1.150×10⁴(T/K)²+3.007×10⁶(T/K)^-1; (298.15≤/K1000). The heat capa-city, the5rst di4erential of{ H₌(T)H₌(298.15 K)} with respectto temperature,is given byC_mp, /J.'K^-1'mol^-1=146.0+2.30×10^-4(T/K)-3.007× 10⁶(T/K)^-2.Thereversibleemf :softhe cell , (-) Pt/NdFeO₃(s)Nd₂O₃(s)Fe(s)]//YDT/CSZ{Fe(s)9FeO:(s)}/Pt(+), were measured in the temperaturerange from 1004 to 1208K. It can be represented within experi-mental error by a linear equation E/V (0.1418±0.0003)-(3.890±0.023)×10^-5(T/K)^-2. The Gibbs energy of formation of solid NdFeO₃ calculated by the least-squares re-gression analysis of the data obtained in the present study, and data for Fe _0.95 O and Nd₂O₃ from the literature, is given by ΔG₌(NdFeO₃,s)/kJ'mol^-1(±2.0) =- 1345.9+ 0.2542(T/K);(1000 ≤ T/K≤41650). The error in ΔG₌(NdFeO₃,s,T ) in-cludes the standard deviation in emf and the uncertainty in the data taken from the literature. Values of ΔH₌(NdFeO₃,s,298.15 K) and S₌(NdFeO₃, s, 298.15 K) calculated by the sec-ond law method are1362.5 (±6) kJ'mol^-1and 123.9 (±2.5)J'K^-1'mol^-1, respectively. Based on the hermodynamic in-formation, an oxygen potential diagram for the system Nd+Fe+O was developed at 1350 K.