Dielectric properties on natural fibres reinforced unsaturated polyester were investigated. Dielectric spectra were measured in the frequency range from 10(-1) Hz to 10(6) Hz and temperature interval from 40 A degrees C to 150 A degrees C. For the composite, three relaxation processes were identified. The first one is the alpha mode relaxation associated with the glass transition of the unsaturated polyester resin matrix. The second relaxation process associated with conductivity occurs as a result of the carriers charges diffusion noted for high temperature above glass transition and low frequencies. As for the third process, it is the interfacial or Maxwell-Wagner-Sillars (MWS) relaxation that is attributable to the accumulation of charges at the natural fibres/polyester resin interfaces. The third relaxation (MWS) was analysed using the Havriliak-Negami model and its intensity was calculated in order to probe the interfacial region between fibres and matrix. This analysis was accomplished by a thorough study of the fibres/matrix interfacial adhesion aspect, by using a differential scanning calorimeter (DSC) and a scanning electron microscope (SEM) observation.