The quality of composite materials based on natural fibres is highly influence by humidity content of the fibres. For a high product quality in the resin-transfer-moulding (RTM) process a constant humidity content has to be achieved. As the moisture content of the fibres can change relative quickly depending on the humidity, measuring moisture content in the mould is beneficial. Near-Infrared-Spectroscopy (NIR) is a widely used tool for moisture content measurement allowing determination of the moisture content within seconds. To do so a calibration model with good accuracy is required. To generate the calibration model NIR spectra of a flax woven fabrics with different moisture content are recorded. These spectra are than treated with chemometric methods to obtain a model with high prediction accuracy. This allows not only monitoring the moisture content of natural fibres with in the mould. Also can the moisture content reduced to an aspired value by applying vacuum to the preheated mould, before starting the resin infusion.