Auramine O was investigated as inhibitor for the corrosion of mild steel in 1.0 M solution of various (sulphuric, hydrochloric, perchloric and phosphoric) acids by studying weight loss, polarisation curves and using electron spectroscopy for chemical analysis technique. Various corrosion parameters such as Tafel slopes, corrosion rate, heat of adsorption and activation energy values were calculated to understand the mechanism of inhibition. Inhibition efficiency increased with increase in concentration of the inhibitor and decreased with increase in temperature. Auramine O was physically adsorbed on the surface of mild steel following Langmuir isotherm and acted as a mixed inhibitor.