The best candidate for the nuclear Sodium-cooled Fast Reactor fuel is the uranium-plutonium mixed dioxide (U,Pu)O2-x. The plutonium content is planned to range between 19% to 40%mol. The fuel has to match various physico-chemical specifications: to be chemically homogeneous, oxygen hypostoichiometric (Oxygen/Metal ratio, with M=(U+Pu), between 1.94 and 2.00)... However, for a Pu content higher than 20%, and an O/M ratio lower than 1.98, at room temperature, the phase diagram of U-Pu-O system exhibits a miscibility gap domain [1]. The sample has then two phases of same structure but different O/M ratios. The demixtion of these two phases triggers the creation of cracks into the material. This phenomenon has to be avoided in order to keep a homogeneous microstructure. The behavior of the microstructure has then to be fully investigated. Recently Talip et al [2] and Elorrieta et al [3] evidenced that Raman spectroscopy is a promising tool for characterizing (U,Pu)O2 materials. Coupled with a microscope, this technique can be used to determine several physico-chemical properties at the grain scale. For instance, the cation distribution homogeneity, the grain size, and the crystal defects can be studied. UO2, PuO2 and (U,Pu)O2 all have the same Fm-3m structure. As the Raman active modes are determined by the symmetry, all these materials have similar Raman spectra. The main band is the T2g, which corresponds to the asymmetrical stretching of the O-O bonds. The position of this band gives information on the chemical composition: O/M ratio, Pu content… Moreover, by studying sintered UO2 samples by Raman cartographies, Maslova et al [4] have evidenced that the T2g intensity is related to the grain orientation. By drawing the T2g intensity map, the grains has been then revealed. In the present work, this technique has been extended to (U,Pu)O2.00 samples. Like in the literature [4], the sample microstructure has been exhibited by performing T2g intensity mapping. Furthermore, the variation in the T2g position, related to the Pu content, has been studied and some heterogeneities in the Pu content were observed at the micrometric scale with the T2g position map. As this characterization tool was first developed for samples with O/M = 2.00, this method can be now extended to oxygen hypostoichiometric samples. The O/M ratio is fixed by heating the sample under reducing atmosphere (Ar/H2 5%). A dedicated device has been specifically designed for in situ Raman measurements [5]. The variation in the microstructure according both the Pu content and the O/M ratio values will be then studied.