Objective To study the inhibiting effect of indole-3-acetic acid (IAA) for mild steel in H2SO4(0. 1 mol/ L) solution so as to reduce the influence of carbon steel production process on the environment. Methods The weight loss experiment, the potentiodynamic polarization test, the electrochemical impedance spectroscopy (EIS) and the scanning electron microscopy (SEM) were conducted to investigate the inhibition efficiency and the mechanism. Results The inhibition efficiency was enhanced with the increasing inhibitor concentration, and the highest inhibition efficiency reached 88. 85% at the inhibitor concentration of 4×10-3 mol/ L. The inhibition efficiency of IAA was lower when the temperature increased, which indicated that IAA was not suitable for high temperature. IAA acted as a mixed-type inhibitor and had a suppressing effect on anodic and cathodic reactions. And there was a competitive adsorption emerged between the adsorbed water molecules and the inhibitor molecules in the process of adsorption effect, which effectively prevented the H+ from crossing, thereby inhibiting the discharge process of the corrosion H+. The adsorption of IAA on carbon steel surface followed the Langmuir adsorption isotherm model, which was spontaneous and was a combination of physical and chemical adsorption. Inhibition of corrosion by inhibiting the active point of the corrosion reaction can improve the activation energy barrier and prevent corrosion of carbon steel. The inhibitor molecules reduced the metal corrosion significantly. Conclusion IAA is a mixed-type corrosion inhibitor, which can inhibit the anodic reaction. It can protect the Q235 carbon steel in 0. 1 mol / L H2 SO4 solution.