The structures of martensites in a Cu-11.2 wt% Al-3 wt% Ni specimen, which was quenched from 1173 K, have been studied by high resolution electron microscopy (HREM) and diffraction techniques. Two kinds of martensites, i.e. beta(1)’ and gamma(1)’, coexisting adjacent to each other in the specimen were observed. The gamma(1)’ matensite consists of microtwins with monoclinic structure. Three variants of the twin structure, i.e. {121}, {210} and {101} twins, are arranged within a single plate. The beta(1)’ martensite possesses basically ordered N9R structure, but mixed with thin 2H domains. Some diffraction spots of this martensite shift along the [001] direction. In addition, extra weak reflections appear in the diffraction pattern due to heterogeneous atomic displacements. The microstructural features of the martensites are examined and discussed.