β-SiC nanoparticles are one of the most common reinforcements in Mg-Al alloy matrix nanocomposites (MgMNCs). The interfacial interactions between β-SiC and the alloy matrix are complex due to the occurrence of new phases and the fine scale of the 3D architecture. This study aims to explore the feasibility of using synchrotron Scanning Transmission X-ray spectro-Microscopy (STXM) to investigate such interfacial interactions and acquire reference X-ray Absorption Spectroscopy (XAS) data for some common interphase crystals present within the composites, which are not readily available. Throughout this study, a reliable procedure for collecting STXM data on samples derived from MgMNCs was developed, and reference XAS spectra for α-Mg, β-Mg17Al12, T2-Al2MgC2, Mg2Si and MgO present in MgMNCs were collected. The accessibility of STXM and spatially resolved XAS spectrum is not only useful for nanocomposite alloy research but applicable widely across the magnesium alloy research community when identifying and quantifying the phases with complex crystal structures and oxide states.