The defect substructure in cold‐worked &bgr; AlNi intermetallic has been examined by means of x‐ray diffraction. The broadenings exhibited by the fundamental and superstructure powder peaks were analyzed in terms of contributions from inhomogeneous strain and planar faults on the 211 and 110 planes. No account was taken of possible contributions from microtwinning. The analysis shows that the pattern of particle size anisotropy exhibited by &bgr; AlNi can be satisfactorily accounted for in terms of certain concentrations ofa/8[110](11¯0)‐anda/6[111] (1¯1¯2)‐typestacking faults, with the former predominating. Possible contribution froma/3[1¯1¯1¯] (1¯1¯2)‐typestacking faults, however, was found to be negligible. Similarly antiphase boundaries were also not found to be important in the cold‐worked structure of stoichiometric AlNi.