The aim of the present work was to develop a surface film on 304L SS filters to increase their corrosion resistance in acid solutions. Film formation was carried out by immersion in sulphuric acid solution containing benzotriazole (BTAH). The filters, after surface treatment, were immersed in a solution of sulphuric acid (3 mol/L). The corrosion behaviour of the filters was evaluated by measurements of open circuit potential at increasing times, electrochemical impedance spectroscopy (EIS) versus time, and polarization curves. The filters surface treated in BTAH containing solutions had significantly more noble corrosion potentials and much lower passive current densities than the bare filters. In addition EIS results indicated stability of the film after a partial attack.