The order‐disorder transition in a polycrystalline specimen of Cu‐32.2 at.% Au has been investigated by means of a high‐temperature x‐ray diffraction method. The experiment confirms the existence of an equilibrium Cu3Au II‐type phase in a temperature interval from 313±3°C to 328±3°C. Diffraction data from this phase are not in conflict with a previously described structure at 31.6 at.% Au based upon an ordered Cu3Au I‐type superlattice in which strictly periodic antiphase domain boundaries occur parallel to any one of the three possible cube faces. Antiphase periods ranging from 18 to 16 are found for the Cu3Au II‐type phase. There is an indication that this period may change as a function of temperature and that periods which are not integral multiples of cubic subcell edges may exist. A two‐phase field between the Cu3Au II‐type and disordered single‐phase regions has been located on the basis of fundamental reflection broadening. Unambiguous evidence for a similar field was not found between the Cu3Au I and Cu3Au II‐type single‐phase fields.