The corrosion behavior of mild steel in two Brønsted acid ionic liquids (BAILs) with different cationic centers triethylammonium and pyridinium-type was electrochemically investigated in non-aqueous and aqueous conditions at 25°C.A relatively wide passivation region (0-2.1 V) was clearly observed for mild steel and a lower corrosion rate was observed for both BAILs at 25°C. The Brønsted acidity of these BAILs is not proportional to corrosion rate of the mild steel therein. In addition the different adsorption centers on each BAIL molecule namely their sulfonate group along with either a quaternary ammonium or pyridinium structural motif means they can possess different inhibiting characteristics as well as modes of adsorption at metal surfaces.Based on these electrochemical results the inhibition ability of both BAILs in 0.5 M HCl solution against acid corrosion of mild steel was investigated at various concentrations at 25°C using gravimetric measurements. The pyridinium-type sulfonate-functionalized IL did not contribute to corrosion protection of the steel surface while the triethylammonium-type sulfonate-functionalized IL had an inhibition efficiency of ca. 40%.Keywords: Corrosion Inhibition HCl BAILs Mild Steel