A polyamide having an equilibrium water absorption of not more than 10% is used as a main material. As a polyamide having an equilibrium water absorption of not.more than 10%, for example, a polyamide comprising a dicarboxylic acid component comprising 60-100 mol % of terephthalic acid and a diamine component comprising 60-100 mol % of 1,9-nonanediamine and/or 2-methyl-1,8-octanediamine is used. As a result, a porous membrane showing extremely small dimensional change even after a hot water treatment, and particularly useful as a medical separation membrane permitting an AC sterilization treatment and the like is obtained.
