In order to investigate the deterioration of low-density polyethylene (LDPE) by partial discharge(PD), experiments were conducted in an air atmosphere containing oxygen. Specimens subjected to PD were examined by atomic force microscope (AFM) and Fourier transform infrared (FTIR) analysis. The AFM images revealed the generation of pits in the deteriorated LDPE specimens, and the FTIR spectra indicated that carbonyl compounds were produced due to the presence of oxygen during PD. It is suggested that the generation of pits by PD is greatly influenced by oxygen content in the atmosphere.