Using the example of an integral-asymmetric isoporous membrane prepared from polystyrene-block-poly(2-hydroxyethyl methacrylate) (PS-b-PHEMA), physical and chemical ways of post-treatment are introduced with the aim to tailor the pore size. These post-treatments are i) thermal annealing and ii) urethane chemistry of ethyl isocyanate (EI) in the presence of perfluoro(methyl cyclohexane). Via these approaches, the pore size of PS-b-PHEMA membranes is successfully tailored in the range of 10-20 nm with narrow pore size distribution by controlling the duration of thermal annealing and chemical reaction, respectively. The excellent hydrophilicity of the PS-b-PHEMA membrane is not changed by thermal annealing. The chemical postmodification using EI is associated with a loss of hydrophilicity with increasing conversion.