It is difficult to prepare stable high internal phase emulsions (HIPEs) of methyl methacrylate (MMA) due to the considerable high solubility of MMA in water phase. Here, we present a facile method to prepare the stable HIPEs of MMA (MMA HIPEs) with the widely used sorbitan monooleate (Span 80) as surfactant just by adding hexadecane (HD) or hydroxyl-terminated polybutadiene (HTPB) as a costabilizer. The different roles of the two long-chain costabilizers (HD and HTPB) to improve the stability of the MMA HIPEs were studied. Poly(methyl methacrylate) porous monoliths were prepared based on the MMA HIPE templates and characterized by field emission scanning electron microscopy, transmission electron microscopy, and N-2 sorption analysis, which showed the formation of highly interconnected pores. Factors that affected the stability of MMA HIPEs and the morphology of polyHIPEs were also investigated.