Abstract The electron charge density distributions ϱ( r) in both Ni-riched Ni 3Al single crystals with and without B-addition have been determined by the TEM-CBED technique and data refinement method in this work. The boron addition introduces the fact that the bonding between the n.n. NiNi pair is anisotropic; the metal bonding between Ni-sitel-Ni of the next n.n. NiNi pair, is strengthened and between Ni-site2-Ni is weakened; the bonding between the n.n. NiAl pair is strengthened and that between Al-sitel-Al (or Al-site2-Al) is weakened. The effects of the change in bonding on the properties and formation of interfaces with preferred structures in the two alloys are discussed.