2-alkyl-N-benzylidenehydrazinecarbothioamide of fatty acid hydrazides from nontraditional oils (neem, rice bran and karanja) have been synthesized and evaluated as corrosion inhibitors for mild steel (MS) in hydrochloric acid (HCl) solution by weight loss method. Adsorption of all Schiff bases on MS surface in acid solution obeyed Temkin's adsorption isotherm. Inhibition efficiency of these compounds increases with increase in concentration of the compound, and vary with solution temperature, immersion time and concentration of acid solution. Various thermodynamic parameters are also calculated to investigate the mechanism of corrosion inhibition.