Natural fibres are envisaged today as potential candidates for replacing glass fibres in composite materials. Although natural fibres have a number of advantages over glass fibres, the strong polar character of their surface is a limiting factor as, compatibility with strongly apolar thermoplastic matrices is very low. Such problems of incompatibility may be overcome with fibre pre-treatments, which can enhance compatibility although having a negative impact on the economics of using such materials. In this study two fibre pre-treatment methods, acetylation and stearic acid treatments, have been applied on flax fibres. The effect of these two pre-treatments has been examined by use of XPS, ToF-SIMS and FTIR spectroscopic methods. It was found that the fibre surface before treatment is very different to what may have been expected for cellulose materials. There is an appreciable coverage of the flax fibre surface with hydrocarbon compounds, possibly waxy substances, but no aromatic compounds were detected. All three spectroscopic methods revealed that the fibre surface chemistry has been altered after the treatments, and especially for acetylation it was found that ester bonds are present on the fibre surface after treatment. For the stearic acid treatment the situation still remains less conclusive. Finally, ToF-SIMS experiments revealed that the coverage of the fibre surface with acetyl groups and stearic acid is highly heterogeneous. (C) 2003 Kluwer Academic Publishers.