Atomic force microscopy (AFM) has been used to investigate the morphology changes in the surface of poly(ethyleneterephthalate) (PET) fabrics due to cold plasma treatments. This has resulted in the possibility to measure quantitatively the root-mean-square (rms) surface roughness and the surface area of the samples developed after the treatment. The morphology changes, mainly rms surface roughness and surface area, on the PET fabrics surface due to air cold plasma have been measured as a function of treatment time and as a function of gas pressure. The same quantities as a function of pressure were measured also for He, Ar, SF₆ and CF₄ gases. The changes in morphology in the cases of air, He and Ar gases seems to be due mainly to etching effects. The situation is different for SF₆ and CF₄ gases where reorganisation of the surface, possibly due to fluorine atoms grafting, seems to be effective.