Abstract: A method of preparing a crystal of a Y-series 123 metal oxide is disclosed, in which a substrate is immersed in a liquid phase which comprises components constituting the metal oxide. The liquid phase contains a solid phase located at a position different from the position at which the substrate contacts the liquid phase. The solid phase provides the liquid phase with solutes which constitute the Y-series 123 metal oxide so that the solutes are transported to the position at which the substrate and the liquid phase contact, thereby permitting the Y-series 123 metal oxide to grow on the substrate as primary crystals.