Structural studies have been performed on precipitation hardening discovered in L1 2 ?orderedNi 3 (Al,Cr) containing 0.2 to 3.0 mol% of carbon using transmission electron microscopy (TEM). Fine octahedral precipitates of M 23 C 6 appeared in the matrix by aging at temperatures around 973 K after solution treatment at 1423 K. TEM examination revealed that the M 23 C 6 phase and the matrix lattices have a cube-cube orientation relationship and keep partial atomic matching at the {111} interface. After prolonged aging or by aging at higher temperatures, the M 23 C 6 precipitates then adopt a rod-like morphology elongated parallel to the directions. Deformation at temperature below 973 K, typical Orowan loops were observed surrounding the M 23 C 6 particles. At higher deformation temperatures, the Orowan loops disappeared and the morphology of dislocations at the particle-matrix interfaces suggested the existence of attractive interaction between dislocations and particles. The change of the interaction modes between dislocation and particles with increasing deformation temperature can be considered as a result of strain relaxation at the interface between matrix and particles.