Graphite oxide (GO) was synthesized from natural graphite powder using Hummers' method. A large number of oxygen-containing functional groups (C–O and CO) on the surface of graphite oxide were obtained, as identified by Fourier-transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The GO material shows outstanding catalytic performance and stability in the selective oxidation of glutaraldehyde to glutaric acid with aqueous H₂O₂. The catalytic activity has a slight increase when the GO is treated with 50% aqueous H₂O₂ solution and decreases evidently when the GO is treated with KBH₄, which could be attributed to the increase in the amount of C–O and CO moieties after oxidation treatment or the decrease in the amount after reduction treatment. The oxygen-containing functional groups on the graphite oxide surface may play an important role in the catalytic process.