PROBLEM TO BE SOLVED: To provide such a porous body formed of polymethyl methacrylate as can be serviceably used as a blood component-separating membrane in an artificial kidney or the like by making use of the structure of minute and uniform pores and as permits the pore diameter control from the order of nanometers to that of micrometers and to provide a method for producing the same.SOLUTION: In a porous body using a polymethyl methacrylate as the principal component, resulting from the spectrum obtained by the measurement with a proton nuclear magnetic resonance, this porous body is characterized in that letting such a repeating unit amount be (A) as is given by one or more kinds of monomers selected from among methacrylic acid, methacrylate formed from methacrylic acid and a 2-16C hydrocarbyl group, acrylic acid, an acrylate formed from acrylic acid and a 1-16C hydrocarbyl group, &alpha-methylstyrene, styrene, maleic anhydride, maleimide, and an N-substituted maleimide, and letting such a repeating unit amount as is given by methyl methacrylate be (B), then (A)/[(A)+(B)] ×100 is 0.00001 or more.
