The thermal and chemical compatibility of silicon nitride ceramics (Si 3 N 4 ) to diamond ensures an adequate adhesion for tribological applications, such as mechanical seals, biomaterials or cutting tools for hard machining operations. Most of the recent research efforts on these components focused on nanocrystalline diamond (NCD) due to its small grain size and surface smoothness.The present study reports for the first time NCD coating of Si 3 N 4 substrates by microwave plasma-assisted chemical vapour deposition (MPACVD) using Ar/H 2 /CH 4 gas mixture and varying the substrate temperature (650–1050 °C) and deposition time. Optimal deposition conditions result in growth rates up to 3.0 μm h −1 that allowed the production of continuous NCD films with low roughness (Ra≈22 nm) and grain size of about 10 nm at the lower temperatures and longer deposition times.