An oxide superconductor of an embodiment includes an oxide superconducting layer including at least one superconducting region containing barium (Ba), copper (Cu) and a first rare earth element, having a continuous perovskite structure, and having a size of 100 nm×100 nm×100 nm or more, and a non-superconducting region in contact with the at least one superconducting region, containing praseodymium (Pr), barium (Ba), copper (Cu), and a second rare earth element, having a ratio of a number of atoms of the praseodymium (Pr) to a sum of a number of atoms of the second rare earth element and the number of atoms of the praseodymium (Pr) being 20% or more, having a continuous perovskite structure continuous with the continuous perovskite structure of the superconducting region, and having a size of 100 nm×100 nm×100 nm or more.