Auger electron (AES), electron energy loss (EELS) and X-ray photoelectron spectroscopy (XPS) were used to identify the reaction products at the fibre-matrix interface in SiC nicalon fibre-LAS (Li2O, Al2O3, SiO2) or LAS + Nb2O5 glass matrix composites. Chemical bonding of the different elements was investigated by AES using sputter-depth profiling on fibres extracted from two matrices by etching in hydrofluoric acid. The chemistry of the silicium was studied by EELS in nicalon-LAS + Nb2O5 composite cross-sections. XPS was performed on fibres extracted from the nicalon-LAS + Nb2O5 composite to confirm EELS and AES results. These investigations show that in both composites the reaction scale at the fibre-matrix interface consists of a carbon layer next to the matrix and of a silicate phase rich in oxygen which contains carbon, probably in the form of a silicon oxycarbide, and which is located between the carbon layer and the fibre core.