Abstract: Porosity of porous crosslinked polystyrenes was examined by the pressurized-mercury intrusion method. Various aftertreatments of those polymers revealed interesting results of behaviors of fixed pores, whichS indicates pores measurable by this method: (1) fixed pores were found to diminish or vanish by swelling them with ethylene dichloride (EDC) as a good solvent or by heating them above the glass transition temperature (Tg), but (2) those pores were observed to reappear after the polymers treated above were swollen again with EDC, followed by replacing EDC with methanol as a poor solvent. This implies that the fixed-pore structure has been memorized like a shape-memory alloy.