Öz Shape memory alloys are characterized by a thermoelastic martensitic transformation and the presence of ordering in the parent phase and martensite. Crystal structure studies of parent and martensite phases in a CuAlMn alloy show that a thermoelastic transformation from an or- nered parent phase of DO3 type to an M18R martensite takes place. This orthorombic structure of M18R form consists of an array of close-packed plaııes. The eighteen layer martensite structure (AB'CB'CA'CA'BA'BC'BC'AC'AB') can form as a result of periodic shifts on the martensite basal plane in the c-direction.