Fracture surfaces of stoichiometric and sub-stoichiometric epoxy, both neat and filled with 0.5 % of inorganic, fullerene-like WS2 nanoparticles (NPs) by mass are investigated with atomic-force microscopy (AFM). Sub-stoichiometric epoxy is very brittle, but other than stoichiometric epoxy, it increases significantly in its fracture toughness with NP addition. For sub-stoichiometric epoxy, AFM investigation revealed a very regular fracture pattern with periodic features normal to the crack propagation direction. Stoichiometric epoxy exhibited ripples several micrometers in size, but nevertheless had a lower fracture surface area. After NP addition, the fracture surfaces were significantly rougher, but the mentioned ripples disappeared. The fracture surface roughness correlated neither to the measured fracture toughness nor to its increase with the nanocomposite's composition.