The interfacial region in an epoxy-aluminum joint has been investigated using a nano-indenter and an atomic force microscope (AFM). The stiffening effect in a soft layer resulting from the restriction of the neighboring harder phase was studied. It is proposed that the region where the indent in the softer material is modified by the harder material can be used to define the indent affected zone (IAZ). The results showed that IAZ was larger than the size of the contact impression of the indentation and increased with increasing indent depth.