Abstract: Polyethylene terephthalate membranes were irradiated by 32S and 79Br ions produced by HI13 tandem accelerator in CIAE. The polymer chains were damaged by the irradiation, and latent tracks were created along the track of the ions. Nanoporous membranes with diameters between 100 and 900 nm were obtained by chemical etching the membranes. To increase the ratio of the velocities of the track etching to the body etching, the membranes were illuminated by ultraviolet light before chemical etching. The conductance measurement was applied to monitor the growing of the pores. The cone angle of pores in membranes irradiated by 79Br is smaller than that by 32S. The pores in the membrane irradiated by 79Br are also more round and uniform in size than that by 32S. 79Br ions are better than 32S ions in making nanoporous membranes.