Abstract: 16 μm polypropylene (PP) films irradiated by ³²S and ⁷⁹Br were sensitized for 6, 8, 10 and 12 h on both sides by UV-irradiation light whose main peak wavelength is 365 nm. The mixed solution of potassium dichromate and sulfuric acid was used as etchant for the film samples. The conductance measurement was applied to monitor the current change with etching time. The breakthrough time of the samples at different sensitization time was measured. With the same ion irradiation, the longer the sensitization time, the faster the etching rate. The relation between sensitization time and the etching rate also depends on the irradiating ions. At the same sensitization time (12 h) and etching conditions, the breakthrough time for samples irradiated by ³²S is 4.8 times of that by ⁷⁹Br.