Polymer nanoporous materials with periodic cylindrical holes were fabricated from microphase-separated structure of diblock copolymers consisting of a radiation-crosslinking polymer and a radiation-degrading polymer through simultaneous crosslinking and degradation by gamma-irradiation. A polybutadiene-block-poly(methyl methacrylate) (PB-b-PMMA) diblock copolymer film that self-assembles into hexagonally packed poly(methyl methacrylate) cylinders in polybutadiene matrix was irradiated with gamma-rays. Solubility test, IR spectroscopy, and TEM and SEM observations for this copolymer film in comparison with a polystyrene-block-poly(methyl methacrylate) diblock copolymer film revealed that poly(methyl methacrylate) domains were removed by gamma-irradiation and succeeding solvent washing to form cylindrical holes within polybutadiene matrix, which was rigidified by radiation crosslinking. Thus, it was demonstrated that nanoporous materials can be prepared by gamma-irradiation, maintaining the original structure of PB-b-PMMA diblock copolymer film. (c) 2007 Wiley Periodicals, Inc.