A technique has been proposed to increase the efficiency of hydrogen production from water by gamma-ray radiolysis as an effective use of radioactive waste. This is possible by putting special metal structures into water to enhance the conversion of mega-electron-volt-range gamma rays to low-energy electrons, which escape from metal into water. The experimental results showed that hydrogen production could be significantly enhanced by carefully controlling the thickness of metal components and the proximity with adjacent metal components. A honeycomb-like structure composed of stainless steel tubes was confirmed to provide the best performance for hydrogen production. These experimental results successfully demonstrated that the modification of metal structure can control the energy and the number of electrons escaping from the metal and actually leads to enhancement of hydrogen production in water.