The epoxy nanocomposites filled with 0.1, 0.5, and 1 wt% nanodiamonds (nanoD) were prepared and their properties were compared with neat epoxy network or epoxy nanocomposite filled with 1 wt% multiwalled carbon nanotubes (MWCNTs). The obtained nanoD-epoxy composites increased significantly thermal stability of prepared nanocomposites in comparison with neat epoxy matrix. The exponential decay of light transmittance with increasing concentration of nanoD in sample was observed. The values of storage modulus G` and glass transition temperature Tg significantly decreased by addition of nanoD to epoxy network. This is caused by inhibition of cross-linking reaction of epoxy- and amino- groups by nanoD.