We produced a type of graphite oxide with the interlayer spacing of 2.09 nm by treating conventional graphite oxide with gamma-rays at an absorbed dose of 200 kGy in air. The expansion of interlayer distance should be attributed to the increased amounts of topological defects and then the improved steric hindrance between interlayers. Due to the decomposition of water molecules in graphite oxide by gamma-rays, the reductive species were produced so that graphite oxide was partially reduced. It is also speculated to be the main mechanisms for alteration of oxygen groups. The change of carbon chain structures and oxygen groups were further supported by X-ray photoelectron spectroscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. This simple and effective method of making graphite oxide with d-spacing of 2.09 nm by irradiating it in air is of interest not only for its easier intercalation and exfoliation than pristine one, but also for its potential to prepare graphene sheets with high percent of monolayers.