Electrochemical frequency modulation, EFM is a new technique for corrosion rate measurements. With the EFM technique, the corrosion rate and corrosion kinetic parameters can be obtained instantaneously without prior knowledge of Tafel slopes, which makes this method an ideal technique for application as a corrosion monitoring tool. Results obtained with the EFM technique were shown to be in agreement with chemical (weight loss) and electrochemical methods (Tafel extrapolation and electrochemical impedance spectroscopy, EIS) for corrosion rate measurements. New synthesized hydrazine carbodithioic acid derivatives namely, N'-furan-2-yl-methylene-hydrazine carbodithioic acid (A), N'-(4-dimethylamino-benzylidene)-hydrazine carbodithioic acid (B) and N'-(3-nitro-benzylidene)-hydrazine carbodithioic acid (C) were examined as corrosion inhibitors for carbon steel in 1 M perchloric acid solution. The results obtained from both chemical and electrochemical measurements show that these compounds suppressed both anodic and cathodic processes of carbon steel corrosion in 1 M HClO4 by adsorption on the electrode surface. The adsorption mode follows the Langmuir adsorption isotherm. The efficiency of the inhibitors increases in the order C > B > A.