The influence of 2H-indeine-1, 3-dione derivatives on C- steel corrosion was studied in 1 M HCl solutions at 30oC. Measurements were conducted using weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and electrochemical frequency modulation (EFM) techniques. These studies have shown that 2H-indeine-1, 3-dione derivatives are mixed-type inhibitors. Corrosion rates obtained from both EFM and EIS methods are comparable with those recorded using Tafel extrapolation method, confirming validation of corrosion rates measured by the latter. The inhibitive action of these 2H-indeine-1, 3-dione derivatives was discussed in terms of blocking the electrode surface by adsorption of the molecules through the active centers contained in their structures following Temkin adsorption isotherm. Quantum chemical method was also employed to explore the relationship between the inhibitor molecular properties and its protection efficiency. The morphology of inhibited and uninhibited C- steel was analyzed by scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX).