The gas-assisted focused ion beam etching characteristics of niobium have been investigated systematically in I-2 and XeF2 gas atmosphere, respectively. The effects of the etching parameters, such as: ion beam current, dwell time, overlap percentage and gas species, on the niobium etching rate and on the gas-assisted etching enhancement have been studied. It was found that the overlap percentage had little effect on the etching characteristics of niobium. It also showed that the I-2 radicals are more reactant with niobium than XeF2 radicals, and to obtain maximum improvement from the gas-assisted etching process one needs to select a smaller ion beam current with a shorter beam dwell time. (c) 2005 American Vacuum Society.