PURPOSE: To obtain a superconductive crystal of high critical temperature by mixing an oxide powder of rare earth element-alkaline earth metal-copper with a copper compound and heating them at a prescribed temperature in an oxygen-containing atmosphere as they are allowed to come into contact with a rare earth element oxide.

CONSTITUTION: An oxide powder which is composed of a rare earth element such as Y, an alkaline earth metal such as Ba, Cu and oxygen, is mixed with a copper compound such as cupric oxide powder or copper naphthenate powder at a weight ratio of 100:(25W400) (calculated the Cu compound as CuO). Then, the mixture is heated in an oxygen-containing gas atmosphere at 950W1,400°C, as the mixture is brought into contact with oxides mainly consisting of rare earth elements such as Y2O3 to give a superconductive crystal of oxide. The resultant oxide superconductive crystal has high critical temperature without reduction in the critical point even in a strong magnetic field.