A TiN nanocoating was deposited on carbon fibres before their consolidation with AZ91E magnesium alloy, provided as a matrix of the composite. The main interest was the interface microstructure. Structural investigations were performed with a FE-SEM Hitachi 3200S scanning electron microscope and a Tecnai G2 FEG high resolution electron microscope equipped with energy dispersive X-ray spectrometer (EDS) and high angle annular dark field (HAADF) detectors. The observations of the fibre-matrix interface revealed the presence of a multilayered zone around the fibres. It consisted of a regular oxide layer with a thickness of approx. 100 nm around the fibre, followed by a titanium-rich layer and a region of longitudinal sharp shaped crystals directed toward the magnesium alloy matrix. This type of interface microstructure suggests that deposition of TiN as a technological nanolayer ensures the proper wettability of fibres by the metal matrix, but does not prevent diffusion processes. It was revealed that both, i.e. diffusion of elements contained in the matrix through the TiN nanolayer and diffusion of oxygen and carbon toward the surface took place.