A new, highly sensitive colorimetry for trace Ni-II at the parts per billion level has been developed. The method is based on effective adsorption of the orange-colored Ni-II chelate with alpha-furil dioxime to a membrane filter. There was superior tolerance to coexistence of high concentration of salts such as sodium nitrate in the trace Ni-II analysis. The proposed method was successfully applied to the NaOH solutions used for the silicon wafer processing and enabled on-site Ni-II analysis which has been urgently needed in the semiconductor manufacturing.