Nanoindentation was used for characterizing epoxy and epoxy/nanodiamond composites at small length scale. The effect of addition of nanodiamond (ND) to epoxy matrix was investigated at micro level through 2D modulus mapping, post and prior being subjected to loading in uniaxial direction. Variation of modulus and the evolution of their distribution with application of stress, was revealed by analysis of maps. thus giving the insight into the role of ND in controlling the mechanical behavior of the epoxy matrix. An improvement of ~ 94% in elastic modulus of epoxy was achieved with 1wt% ND. Finite element method (FEM) of the representative volume element (RVE) was used to evaluate effect of ND in stiffening epoxy matrix. There is a close agreement between predicted and experimental results. With 0.3 wt% ND the tensile strength of epoxy showed an improvement of ~ 56% along with improvement of ~66% in % strain (at break). Interfacial interaction, dispersion and strengthening mechanisms was evaluated thoroughly using transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM). © 2019 International Committee on Composite Materials. All rights reserved.