Superconductors having a composition Bi.sub.2-a-b-c Sn.sub.a Pb.sub.b Sb.sub.c Sr.sub.2 Ca.sub.n-1 Cu.sub.n O.sub.2n+4 can be made by firing the appropriate mixtures of designated oxides or carbonates. In the composition a=about 0.001-0.4, b about 0-0.4, c about 0-0.4, and n 2 or 3. The addition of Sn improves the superconductive properties of comparable compositions that lack Sn. For example, Bi.sub.1.6 Sn.sub.0.4 Sr.sub.2 Ca.sub.2 Cu.sub.3 O.sub.x (x=ca 10), calcined at 830.degree. C. for 15 hours shows superconductivity by magnetic susceptibility tests at about 77.degree. K. whereas Bi.sub.2 Sr.sub.2 Ca.sub.2 Cu.sub.3 O.sub.10 prepared under the same conditions but lacking Sn, shows nothing at this temperature.