Iron (Fe) nano-polycrystalline metal obtained by sintering reduced iron nanoparticles from iron oxide was applied to an axial flux generator. When the thickness of the core material is 1/10, it has the same ability of the power generation as when Fe bulk is used as the core. We can also reduce the iron loss (hysteresis loss and eddy current loss), which enables the construction of thin and axial flux generators with light weight. We investigated the magnetization property of the core inductor at the direct current and found that Fe nanoparticles were produced from iron oxide particles by high voltage pulse or laser ablation in liquids. Core inductors with these materials were fabricated. It has been clarified from measurements of the core inductor magnetization that the relative permeability of the sintered Fe nanopolycrystalline was one million.