Irradiation effects of 30 keV proton implanted polyaniline (PAn) have been studied. PAn was synthesized by standard MacDiarmid method and the implantation of low energy (30 keV) proton beam on PAn was performed at room-temperature, ion fluence varied from 7.5 x 10'4ions/cm2 to 2.25 x lOI ions/cm2. Electrical conductivities 0 of PAn decreased according to the increase of radiation dose, and the value of CT lowered to about one third after irradiation (from 2.6 to 0.77 S/cm). IR spectra of PAn before and after irradiation gave significant difference at 1625 cm-' and within the region 1118-584 cm-', where the height of many peaks reduced, these results indicate that C=N bonds were broken and the C-H bending modes of benzenoid structure sustained great variations. The decrease of force factors might be attributed to destruction of benzenoid structure by implanted protons and scission of C&N conjugale bonds. The colour of PAn surface changed from dark-blue to yellow (with metallic-luster) after irradiation, which indicate that carbonization took place. Although both chain-scission and carbonization were induced, the predominant process is chain-s&ion, which resulted in the decrease of electrical conductivity.