Reactive ion beam etching of polyimide thin films was investigated using x‐ray photoelectron spectroscopy (XPS) and etch rate measurements. The etching mechanism and the near surface damage produced in polyimide by exposure to argon and oxygen ion beams were compared. The etch rate of polyimide by oxygen ions was studied as a function of ion current density and neutral oxygen molecular flux, and the results were found to match a model for the contribution of neutral fluxes to the etch process. Ion beam etching with inert argon ions was found to produce a graphitelike layer on polyimide. Reactive ion beam etching with oxygen ions resulted in much faster etching than for argon ions, and did not produce a graphitized layer.