Porous copolymer beads of 2,3-epoxypropyl methacrylate (glycidyl methacrylate, GMA) crosslinked with 2-ethyl-2-(hydroxymethyl)-propan-1,3-diol trimethacrylate (trimethylolpropane trimethacrylate, TRIM) were prepared with toluene and octan-2-one as porogens by suspension polymerization. With an increase in the ratio of porogen to monomer, the total pore volume of poly(GHA-co-TRIM) increases significantly, whereas the surface area hardly changes. The total pore volume also depends on the nature of the porogen, exhibiting a maximum at the larger GMA contents in the monomer mixture of 50% v/v with octan-2-one and of 60% v/v with toluene, compared to that at the GMA content of 25% v/v with a 9/1 v/v mixture of cyclohexanol and dodecan-1-ol [Verweij, P. D.; Sherrington, D. C. J Mater Chem 1991, 1 (3), 371]. The surface area decreases significantly with an increase in the ratio of GMA to TRIM, almost regardless of the nature of the porogen. The porous properties of poly(GMA-co-TRIM) was well explained on the basis of phase separation, particularly taking into account not only the solubility parameters of the resulting polymer network and porogen but also the rigidity of TRIM. The porous poly(GMA-co-TRIM) may be a promising polymer matrix of novel materials for separation of boron isotopes.