Differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) studies have been performed to reveal a crosslinked epoxy nature of the spherical particles formed in cured epoxy/DDS/PMMA blends. An interesting phase inversion phenomenon was observed in cured DGEBA/DDS/PMMA blends, which occurred at a relatively low thermoplastic composition of 20 phr PMMA in blends. A unique method of preparing crosslinked epoxy spheres of controlled sizes based on cure-induced phase inversion is described in this report. Several factors have been found to affect the geometry of the formed epoxy spheres. The volume fraction of PMMA in the blends strongly dominates the influence. With the increase of PMMA volume fraction in the blends, the spheres not only become smaller in sizes, but also more regular in the spherical geometry due to less impingement. The crosslinking density (DDS phr in the blends) has been found to influence the average sizes of the spheres. The cure temperature has relatively limited effects only when the PMMA loadings in the blends are relatively small. Various potential applications for the epoxy microspheres may be investigated in future studies.