The effects of plasma treatment by atmospheric low temperature pulse discharge and microwave discharge, used to increase adhesion strength between polyester fibres and a rubber matrix, were investigated and compared. Morphological changes as a result of plasma treatment were observed using scanning electron microscopy (SEM). The differences in Hg-porosity suggest that plasma treatment has a substantial effect on the interlocking of the rubber matrix into the PET fibres. The chemical changes were determined by X-ray photoelectron spectroscopy (XPS) method. These studies have also shown that the surface population of chemical species formed after microwave-plasma treatment is dependent on the plasma gas.