The change in mechanical properties induced by irradiation of electron (2 MeV), proton (10 and 20 MeV), He2+ (20 and 50 MeV), and 220 MeV C5+ ions were studied for polymer films of polyethylene (PE), bis-phenol A based polysulphone (PSF) and polyethersulphone (PES). There is no difference between the irradiations of proton and electron in the mechanical properties for PE compared by absorbed dose. On the contrary, in aromatic polymers as PES and PSF, the decrement in the tensile strength and elongation with dose is extremely depressed in the irradiation of ion. It was found from the measurements of gel fraction and glass transition temperature that the probability of crosslinking and/or chain scission depends on linear energy transfer (LET).