Miniemulsion polymerization of methyl methacrylate has been conducted employing Shirasu porous glass (SPG) membrane emulsification for the generation of the initial miniemulsion. For the first time, submicron-sized monomer droplets and polymer particles have been prepared using membranes with pore sizes significantly smaller than those previously reported. Membrane pore sizes of diameters 100?400 nm were explored, demonstrating that the final particle size can be conveniently tuned within the diameter range of 250?1600 nm. The choice of radical initiator is crucial: a sufficiently hydrophobic initiator (lauroyl peroxide) is required to minimize the generation of bimodal particle size distributions via secondary nucleation. Given the advantages of low energy consumption, reduced shear stress (compared with conventional high-energy mixing approaches such as ultrasonication), and an easily adjustable particle size via the membrane pore size, membrane emulsification has significant potential for the synthesis of polymeric nanoparticles via miniemulsion polymerization.