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The continuous growth of the composites industry accompanied by the use of emerging new materials and even more complex shapes and structures cause increasing difficulties in design, production and maintenance of composite products. One issue is the insufficient knowledge about the cure kinetics of the composites during the production phase, which directly results in some imperfectly cured composite parts. Another issue is the insufficient knowledge about the structural health of the composites, for instance the ageing, during the operation phase. In this paper, current progress in the development of a dielectric sensor system for the on-line cure monitoring of composites is presented. The dielectric sensor was fabricated by Printed Circuit Board (PCB) technology on a flexible substrate into a final interdigital structure. The dielectric properties of the resin, which were monitored by the interdigital sensor, changed during the curing. By analysing the dielectric data (relative permittivity, and loss factor), the degree of the cure can be understood. The data obtained in the experiments clearly showed the different stages of the cure, which can be used with confidence as a tool for the monitoring of the composite cure. [ABSTRACT FROM AUTHOR]