Body-centred cubic β brass, containing ca. 40% Zn, obtained by quenching from 850°∼900°C. shows reversal process of Kurdjumow and Sachs type transformation during tempering. Various intermediate structures between β and face-centred cubic α were ascertained by means of X-ray analysis using capillary and ordinary X-ray tubes. Such are body-centred and face-centred tetragonal structures having various axial ratios; therefore the transformation must take, place with gradual manner, although the formation of martenstic needles are well known. The decrease of solubility of Zn in a solid solution due to lowering of the temperature, determined from X-ray data, is more significant than of Konobejewski.