The invention provides a catalyst for electrodes in solid-polymer fuel cells which comprises metal oxide particles themselves. The invention can be used as a substituent for the carbon particles having platinum deposited thereon and platinum metal particles which are presently in general use as, e.g., a catalyst for electrodes in fuel cells, and has a possibility that the amount of platinum to be used can be greatly reduced as compared with the conventional carbon particles having platinum deposited thereon, etc. The catalyst comprises fine transition-metal oxide particles having, in the main phase, a perovskite structure represented by the general formula ABO 3 (wherein A represents one or more elements selected among lanthanum, strontium, cerium, calcium, yttrium, erbium, praseodymium, neodymium, samarium, europium, silicon, magnesium, barium, niobium, lead, bismuth, and antimony; and B represents one or more elements selected among iron, cobalt, manganese, copper, titanium, chromium, nickel, and molybdenum), the fine oxide particles having lattice constants satisfying the following relationship (1): 1.402<2b/a+c<1.422 wherein a and c represent the minor-axis lengths of the perovskite type crystal lattice and b represents the major-axis length thereof.