The efficiency of tin(II) 2-ethylhexanoate catalyst and hydrophilic silica nanoparticles in compatibilizing polycarbonate/poly(methyl methacrylate) (PMMA/PC) blends were compared in terms of the morphological, thermal, and mechanical properties. Both the catalyst and nanoparticles were found to refine the morphology of PMMA/PC blends. Although the blends with catalyst exhibited smaller phase size, they possessed more deteriorated mechanical performance and worse thermal properties than those of nanoparticle-filled ones due to the significant degradation during transesterification reactions. The addition of nanoparticles refined the morphology of PMMA/PC blends kinetically to a lesser extent. However, the thermal and mechanical properties of blends were improved noticeably upon the addition of nanoparticles. Finally, the mechanisms, advantages, and disadvantages of catalyst and nanoparticles in compatibilizing PMMA/PC blends were discussed and compared.