The introduction of (U,Am)O2±x materials in the Fast Neutron Reactors requires a detailed knowledge of their physico-chemical properties to predict their behaviour under both normal and off-normal conditions. The melting temperature (Tm) is among the fundamental parameters to determine the safety limits of a fuel. We performed Tm measurements under both inert atmosphere (argon) and under air on (U1-y,Amy)O2±x samples with 0.075≤y≤0.7 using a laser-heating coupled with fast pyrometry technique [1]. For all the compositions, the Tm measurements under argon were reproducible. An almost linear decrease from 3080 K to 2900 K as a function of the Am/(Am+U) ratio was found. A different behaviour was observed under air. For the samples with 0.075≤y<0.2, the Tm decreased during the first consecutive laser shots and then it stabilized to values 400-500 K lower than under Ar. This behaviour is identified as an effect of the Oxygen/Metal ratio increase and possibly the formation of hyper-stoichiometric oxides such as M3O8. On the contrary, for the highest Am contents, the measured Tm values were close to those under Ar, and no variation was observed in the consecutive attempts. Various post-melting characterizations (XRD, XAS, SEM) were performed to determine the composition (O/M ratio and Am/(Am+U) using XAS) and the phases present (XRD) in the samples after the measurements. Besides, in order to understand the oxidation process of (U,Am)O2±x under air, high temperature XRD measurements were performed from room temperature up to 1800 K. The results showed that the Am stabilizes the (U,Am)O2±x fluorite structure toward the oxidation, in agreement with the melting temperature measurements.