The invention relates to a high-temperature superconductor composed of the oxides of bismuth, strontium, calcium and copper and, optionally, of lead, and having the composition Bi.sub.2-a+b+c Pb.sub.a (Sr, Ca).sub.3-b-c Cu.sub.2+d O.sub.x, where a=0 to 0.7; b+c=0 to 0.5; d=-0.1 to 0.1 and x=7 to 10 and a Sr:Ca ratio of 2.8:1 to 1:2.8 as well as of strontium and/or barium sulfates. Said superconductor can be prepared by intimately mixing the oxides of bismuth, strontium, calcium and copper and optionally of lead with strontium and/or barium sulfates, melting the mixture by heating to temperatures of 870 to 1300.degree. C., higher temperatures being required for higher strontium and/or barium sulfate contents, pouring the melt into molds and allowing it to solidify slowly therein and subjecting the moldings removed from the molds to a heat treatment at temperatures of 700 to 900.degree. C. in an oxygen-containing atmosphere.