The inhibition effect of a new composite organic inhibitor (named IMC-16) on the corrosion of steel rebar in simulated concrete solutions or inside mortar specimens was investigated by means of half-cell corrosion potential measurement, linear polarization measurement and electrochemical impendence spectroscopy respectively. For the comparison, the inhibition effect of a conventional inhibitor Ca(NO₂)₂ was also presented. Results indicate that whether in simulated concrete solutions or inside mortar specimens,for the case of blank, the corrosion potentials of steel rebar electrodes gradually reduced, while the corrosion current densities significantly increased, indicating that the passivity of steel rebar was deteriorated and the localized corrosion initiated on the surface of steel rebar electrodes due to the aggressive effect of chloride ions. However, after the addition of IMC-16 inhibitor, the corrosion potentials and the impedance modulus of steel rebar electrodes were obviously increased, the corrosion current densities and double layer capacitances largely decreased in comparison with those of blank, which reveal that the corrosion of steel rebar was well controlled, the composite organic inhibitor had excellent inhibition effect for the chloride-induced corrosion, and the onset time of steel rebar corrosion was effectively delayed. Dry and wet cycle experiments further show that Ca(NO₂)₂ could retard the steel rebar corrosion at the early stage of tests, but its inhibition performance was gradually decreased with the process of experiments. In comparison with Ca(NO₂)₂, although the inhibition effect of IMC-16 inhibitor was not enough to prevent the steel rebar from corrosion at the early stage of tests, but its inhibition effect and stability were much better than those of Ca(NO₂)₂ at the same concentration for long term.