Résumé : We report the first nanoindentation studies of well-ordered nanocrystal supercrystals composed of 7 nm lead sulfide nanocrystals stabilized with oleic acid ligands as a model system Their modulus and hardness were found to be similar to hard polymers at 17 GPa and 70 MPa, respectively, and the fracture toughness was 40 KPa/m(1/2), revealing the brittle nature of these materials The mechanical properties arc dominated by the organic capping agents surrounding the inorganic cores The close-packed structure distributes stress evenly increasing the modulus and hardness The relatively short ligands are not likely to be highly interdigitated leading to low dissipation during crack propagation and a low-fracture toughness value