A reaction mixture was developed for formation of soft organic monolith that was easily smashed, rinsed, refluxed, filtered, and dried to give monolith particles having high pore volume of macropores. This phase was almost without mesopores. The reaction mixture was composed of methacrylic acid, ethylene glycol dimethacrylate, polyethylene glycol (porogen), and an initiator in a mixed solvent of toluene and isooctane. The selection of porogen and its amount was carefully carried out to obtain the optimized separation efficiency of the resultant phase. The median macropore size was 1.6 mu m, and the total pore volume was 3.0-3.4 mL/g. The median particle size (volume based) was 15 mu m, and the range of particle size distribution was very broad. Nevertheless the column (1 x 300 mm) packed with this phase showed good separation efficiency (N similar to 10,000-16,000) comparable to that of a commercial column packed with 5 mu m C18 silica particles.