A superconductor comprising oxides of rhenium, barium and copper or an assembly thereof, wherein crystal orientations of the (123) phase in the matrix are aligned and there is no large tilt boundary having a difference in orientation of 20° or above and the (211) phase has a finely dispersed structure. It is shaped in sheet or wire form and the c axes of the crystals of the shaped article are aligned at an angle of ±30° or less or in a range of 60 to 120° with respect to a normal of the plane of the shaped article. This superconductor is produced by placing the shaped article in a heating furnace and shifting a temperature zone wherein grains are formed in the (123) phase of the matrix of the shaped article, i.e. a temperature zone of 1050 to 910°C having a gradient of at least 2°C starting with one end of the shaped article toward the other end thereof at a rate of 0.4 cm/h or less.