The subsolidus portion of the system CdO‐PbO‐O was investigated at high temperatures and oxygen pressures in cold‐seal pressure vessels. Specially prepared cadmium hydroxide precipitate was used to achieve reaction equilibria. Two ternary oxide phases exist in the system: Cd2PbO4is stable under all conditions investigated; CdPb2O5dissociates (2CdPb2O5⇋ Cd2PbO4+Pb3O4+O2). The P‐T univariant curve was mapped. Compatibility triangles illustrate the phase equilibria of the system. Cell constants for Cd2PbO4are:a0=5.671,b0=9.902,C0= 3.139, all ±0.001 Å. The space group was determined asPbam(Pba2); Cd2PbO4is isostructural with the Sr2PbO4structure type. Derived average metal‐oxygen distances are: Cd–O 2.35 and Pb–O 2.08 Å. The structure of C