Internal interfaces in two ceramic systems, monolithic Si3N4 (SN) and TiN-dispersed Si3N4 nanocomposite (STN), were characterized by analytical transmission electron microscopy (TEM). In monolithic SN both MgO and Y2O3 dopants are preferentially hosted by the vitreous intergranular phase in pockets at triple grain junctions (TJ), whereas in STN composites the highest dopant concentrations were observed in grain and phase boundaries. The width of grain boundary films, as revealed by high-resolution TEM imaging, varied between approximate to 0.8 nm in monolithic SN and approximate to 1.0-1.2 nm in STN. Intergranular films with increased width approximate to 1.8 nm were detected in SN-TiN phase boundaries. Although no enrichment of Ti could be detected in the intergranular phase, it appears that the presence of TiN dispersants; indirectly contributes to the intergranular phase formation. It is assumed that TiO2 impurities sitting on TiN particle surfaces react with the matrix phase, resulting in a more oxidic nature of intergranular films due to increased SiO2 Supply in intergranular regions. Phase-specific Si-L-2,L-3 energy-loss near edge structure features, which could serve as fingerprints for phase identification, were observed in spatial-difference electron energy-loss spectra from grain boundary films and TJ pockets.