Disclosed is an oxide superconductor comprising an oxide of RE, Ba and Cu, which consists of a superconductor having a texture wherein the crystal directions of the 123 phase in the matrix are uniform, large angle grain boundaries having an directional difference larger than 20.degree. are not present and the 211 phase is finely dispersed, or an aggregate thereof, wherein the superconductor is formed into a plate or wire and the c-axis of the crystal of the formed body is uniform within .+-.30.degree. to the normal of the plate face of the formed body or in the range of from 60.degree. to 120.degree. to said normal. Also disclosed is a process for the preparation of an oxide superconductor as set forth above, which comprises inserting a formed body as mentioned above to a heating furnace and moving a region of a temperature at which grains are formed in the 123 phase of the matrix of the formed body, i.e., through a region having a temperature of from 1050.degree. to 910.degree. C., having a temperature gradient of at least 2.degree. C./cm, at a speed lower than 0.4 cm/hr from the top end of the formed body to the rear and thereof.