High osmotic pressure chromatography (HOPC), recently developed to separate a large amount of polydisperse polymer with respect to molecular weight, was carried out by using controlled-pore glasses (CPG) as separating media. HOPC is based on the partitioning of a polymer solution with a porous medium specific to high concentrations that exert a high osmotic pressure. The molecular weight distributions of the initial fractions separated were much narrower compared with those obtained by using silica gels, as CPG has a narrower distribution in the pore size. Furthermore, CPG with a larger pore size produced initial fractions with a higher molecular weight, thereby demonstrating that HOPC works on the basis of size exclusion even at high concentrations. The separation was optimal when the ratio of the radius of gyration of the injected polymer to the pore radius was between 1 and 2. The ratio is several times as large as the one commonly used in gel permeation chromatography