Provided is an oxide superconductor composition that makes it possible to increase film thickness, increase production speed, and decrease costs when producing a REBaCuO-type oxide superconductor wire (wherein RE is at least one element selected from the group consisting of Y, Nd, Sm, Gd, Dy, Eu, Er, Yb, Pr, and Ho). The oxide superconductor comprises, as essential components thereof, an RE salt of a carboxylic acid that serves as an RE component, that does not contain a ketone group, and that has 3-8 carbon atoms, barium trifluoroacetate that serves as a Ba component, one or more copper salts that serve as a Cu component and that are selected from the group consisting of copper salts of branched saturated aliphatic carboxylic acids having 6-16 carbon atoms and copper salts of alicyclic carboxylic acids having 6-16 carbon atoms, and an organic solvent that dissolves the aforementioned metal salt components.