The synthesis by semicontinuous heterophase polymerization and the characterization of mesoporous crosslinked polystyrene particles in the nanometer range (ca. 30 nm) are reported here. The particles have pores between 6 and 8 nm in diameter and pore volume around 0.40 cm(3)/g. In spite that the polymerization was not carried out at highly monomer-starved conditions, particles with narrow size distribution were obtained, which is ascribed to inter-particle hetero-coagulation at latter stages of polymerization, due to lack of enough surfactant to cover all the particles even before 45% global conversion.