A mechanothermal synthesis of orthorhombic perovskite oxide (YFeO 3 ) is proposed that starts from equimolar mixtures of Y(CH 3 COO) 3 ·4H 2 O and FeC 2 O 4 ·2H 2 O subjected to mechanical activation by high energy milling. The course of the decomposition process has been studied by thermoanalysis (TG/DSC) showing that, after dehydration, the decomposition occurs, through the formation of an intermediate carbonaceous phase (Y 2 O 2 CO 3 ), leading to YFeO 3 only when starting from the milled mixtures. Annealing in air the activated mixture in the temperature range between 400 and 900°C shows that crystalline YFeO 3 is obtained only for annealing temperatures T≥650°C: this has been confirmed both by XRD and FT-IR measurements. On the other hand TG/DSC experiments performed on YFeO 3 obtained by annealing at T≥400°C show a slight mass loss accompanied by an exothermic DSC peak, very likely due to the decomposition of the intermediate Y 2 O(CO 3 ) 2 , for all the samples annealed at T≤600°C. All the heat capacity data derived from measurements of temperature modulated DSC show the Neel temperature. However reproducible C P data have been obtained only for the samples annealed 8h at T≥750°C. As a matter of fact XRPD of samples of physical mixture show that the formation of YFeO 3 is only completed by a 250h treatment at 1300°C. What happens is that the phase Y 3 Fe 5 O 12 forms at 1100°C and such a phase only very slowly reacts (at T>1100°C) with Y 2 O 3 to transform to YFeO 3 .