The microstructure of novel AZ91 magnesium matrix composite reinforced with glassy carbon particles has been characterized in this study. The composite was produced by hot pressing a mixture of glassy carbon particles and metal powder. Beforehand, the particles were coated with SiO2 by a sol-gel method. Metris X-tek and Xradia MicroXCT laboratory X-ray tomography systems were used to obtain 3D microstructural information (particle-size distribution, volume fraction of particles, phase formation and defects in the form of clusters of particles and pores). These 3D features were validated by 2D scanning electron microscopy (SEM) methods.