In order to determine the structure of short range order which develops on heating the deformed αCu–Al alloys and to obtain informations on the relationship between short range order and anneal-hardening, the change in microscopic structures of deformed alloys during heat treatment was investigated by hardness measurement, electron microscopy and diffraction. Annealing of the deformed specimens gives rise to a development of short range order accompanied with an increase in hardness. It was found that anneal-hardening could be closely associated with the defects introduced by the deformation and with the short range order. The complicated diffraction patterns observed in the specimen before recrystallization can be interpreted as being due to stacking faults and twins including the effect of double diffraction as well as due to the short range order. A model for the microstructure with the short range order was proposed and the composition dependence of the peak position of diffuse scattering was interpreted by the Fermi-surface-imaging theory.