Selected hydrazides of fatty acids with C-9-C-17 carbon atoms have been synthesized and evaluated as corrosion inhibitors of mild steel (MS) in hydrochloric acid (HCl) solutions by weight loss and potentiodynamic polarization methods. The adsorption of all the hydrazides on mild steel surface in the acid solution has been found to obey Langmuir's adsorption isotherm. The potentiodynamic polarization studies revealed that all compounds block the corrosion reactions. Inhibition efficiency (IE) of these compounds has been found to vary with the concentration of the compound, solution temperature, immersion time and concentration of the acid solution. The values of activation energy (E-a) and free energy of adsorption (Delta G(ads)) have been calculated to investigate the mechanism of the corrosion inhibition.