NOVELTY - Preparing pyrochlore-type oxide involves forming precipitate of pyrochlore-type oxide by reaction of halide or nitrate of metal element (A) and alkaline metal acid of metal element (B'); and calcining the precipitate of oxide at a temperature of at least 250 degrees C to at most 900 degrees C. The metal element (A) contains A1 that is at least one element selected from lead (Pb), tin (Sn), and zinc (Zn), and metal element B' contains B1 that is at least one element selected from ruthenium (Ru), tungsten (W), molybdenum (Mo), iridium (Ir), rhodium (Rh), manganese (Mn), chromium (Cr), and rhenium (Re).    USE - For preparing a pyrochlore-type oxide used for producing an electrocatalyst for a fuel cell (claimed) that generates electricity through electrochemical reaction between hydrogen and oxygen; and as a catalyst for promoting an electrode reaction.    ADVANTAGE - The method efficiently removes impurities through washing and drying processes, and allows calcination of the pyrochlore-type oxide under controlled conditions. This allows the crystallinity of the pyrochlore-type oxide, which contained amorphous parts immediately after the production of the precipitate, to be increased so that the resistance to acid can be improved while preventing particle aggregation. The method shows improvement in terms of resistance to dissolving of the catalyst and in terms of maintaining an oxygen reduction reaction (ORR) activity. The method allows preparation of pyrochlore-type oxide catalyst that has a large specific surface area and high crystallinity. By using the method, pyrochlore-type oxide catalyst can be produced at approximate room temperature in a liquid phase. The electric conductivity suitable for electrode reaction can be maintained by using as electrode catalyst, a pyrochlore-type oxide mixed with a solid conductive material such as carbon, and a void is ensured that is used for spreading a reactive gas such as a fuel gas or an oxidant gas. Therefore, the further improvement of the oxygen reduction activity of an obtained electrode catalyst can be ensured.    DETAILED DESCRIPTION - A method (M1) for preparing a pyrochlore-type oxide of formula A2B'2O7-z (I) involves: forming a precipitate of the pyrochlore-type oxide by a reaction of a halide or nitrate of the A and an alkaline metal acid of the B'; and calcining the precipitate of the pyrochlore-type oxide at a temperature of at least 250 degrees C to at most 900 degrees C. The metal element A contains A1 that is at least one element selected from Pb, Sn, and Zn, and metal element B' contains B1 that is at least one element selected from Ru, W, Mo, Ir, Rh, Mn, Cr, and Re.    A and B'=a metal element;    z=at least 0 to at most 1.    An INDEPENDENT CLAIM is included for a method (M2) for producing an electrocatalyst for a fuel cell that contains pyrochlore-type oxide of formula (I) involving: forming a precipitate by a reaction of a halide or nitrate of the A and an alkaline metal acid of the B'; and calcining the precipitate of the pyrochlore-type oxide at a temperature of at least 250 degrees C to at most 900 degrees C in an inert gas atmosphere such as nitrogen.