Four organic inhibitors namely, 4-amino-3-methyl-5-mercapto-1,2,4-triazole (AMMT), 4-amino-3-ethyl-5-mercapto-1,2,4-triazole (AEMT), 4-amino-3-propyl-5-mercapto-1,2,4-triazole (APMT) and 4-amino-3-butyl-5-mercapto-1,2,4-triazole (ABMT) were synthesized to investigate their inhibiting actions on corrosion of mild steel (MS) in aqueous Solutions containing 20% formic acid and 20% acetic acid by weight loss and potentiodynamic polarization methods. All of these compounds have shown good inhibition efficiency (IE) in the formic acid and acetic acid solutions. IE of these compounds has been found to vary with the concentration of the compounds, temperature, immersion time and concentration of acid Solutions. The adsorption of these compounds on the mild steel surface from both the acids has been found to obey Langmuir adsorption isotherm. The values of activation energy (E-a) and free energy of adsorption (DeltaG(ads)) indicated physical adsorption of these compounds on the steel surface. The potentiodynamic polarization experiments revealed that all the Compounds are mixed type inhibitors.