The oxidation of a MoSi2 composite was studied in dry air, oxygen and oxygen saturated with 10% water vapour at 450 degreesC. The kinetics were investigated using TGA as well as oxide thickness measurements. Detailed analyses were performed on the morphology and composition of the oxide using XRD, ESEM, SEM, and EDX. It is shown that the oxidation rate increases drastically in the presence of water vapour, and the growth Of MoO3 crystals on the oxide surface increases considerably. The different re.-ions in the oxide cross-section are Mo-depleted compared with the corresponding regions in the bulk when oxidised in oxygen saturated with 10% water vapour. However., the samples oxidised in dry oxygen only shows Mo-depletion in some outer parts of the oxide. Accelerated growth of the MoSi2-oxide layer during exposure in O-2+10%H2O compared to that in O-2 can be related to the fact that more volatile Mo-species form in the presence of water vapour, resulting in a substantial loss of MoO3 from the inner part of the oxide. The voids left behind are not healed by the silica at this low temperature, which leaves the oxide with an open structure. As a result, the oxidation rate increases.