Four sulfur-containing and three nitrogen-containing organic compounds have been tested as inhibitors for four different austenitic stainless steels-SS304, S5316, SS317L, and SS41O-in 10-50 weight% sulfuric acid solutions respectively. Results confirmed that the sulfur-containing compounds were more effective than the nitrogen-containing compounds. The effect of sodium iodide additions on the behaviours of two of the nitrogen-containing compounds was also studied. The synergistic effect caused by the 1 ion was essential for nitrogen-containing compounds as inhibitors in sulfuric acid solution.