A new corrosion inhibitor namely, 4-salicylideneamino-3-hydrazino-5-mercapto-1,2,4-triazole (SAHMT), has been synthesized and its influence on corrosion inhibition of oil-well tubular steel (N-80) and mild steel in 15% hydrochloric acid (HCl) solution under boiling condition has been studied using weight loss method. Potentiodynamic polarization measurements clearly reveal that the investigated inhibitor is of mixed type and it inhibits the corrosion of both the steels by blocking the active site of the metal. The adsorption of the inhibitor on the metal surface from 15% HCl has been found to obey Temkin's adsorption isotherm. The performance of the SAHMT was compared with that of propargyl alcohol (PA), a standard corrosion inhibitor for acidization.