The characteristics of mart ensitic transformation and martensite substructures in Ni(Cu)Al alloys containing up to 10 atomic percent Cu were studied. The crystallographic structure of a1l the Ni(Cu)Al martensites was identified to AuCu(I) type and their c/a ratios were decreased with increasing Cu content. Other effects of Cu substitution were as follows : The invariant shear strain was increased up to 0.163 from the near ideal value of 0.129 in NiAl alloy. Hardness of Ni(Cu)Al martensite decreased to 300㎏/㎟from 720㎏/㎟, the hardness of NiAl martensite. Martensite morphologies of Ni(Cu) Al alloys are quite similar to that of NiAl alloys but crossed morphologies are quite often observed in Ni(Cu)Al martensites. Tweed structure was also observed in Ni(Cu)Al alloys.