Thiosemicarbazide derivatives have been used as inhibitors for corrosion of steel in acidic medium by weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and electrochemical frequency modulation (EFM) techniques. Poteniodynamic polarization measurements means that they acts as a type of chemical inhibitors .The inhibition efficiency increases with increasing the inhibitor concentration, and also increase with increasing the temperature. The adsorption of thiosemicarbazide derivatives on the surface of carbon steel obeys Langmuir’s adsorption isotherm. From EFM the causality factors are very close to theoretical values which indicate that the measured data are of good quality. Nyquist plots show a single capacitive loop in uninhibited and inhibited solutions.