Improvement in a method for producing superconductors of thallium (T1) type compound oxides by sintering a material powder mixture including at least one thallium-containing powder, the method including wrapping the material powder mixture in a foil of precious metals or their alloys and placing the wrapped material powder in a pipe of precious metals or their alloys and having an opening, wherein the material powder mixture wrapped in the foil is sintered in the pipe while oxygen gas is supplied into the pipe through the opening.