Effects, Of roar Corrosion inhibitors namely, 4-(N, N-dimethylamino) benzylidine imino-3-propyl-5-rnercapto-1,2,4-triazole(DIPMT), 4-benzylidine imino-3-propyl-5-mercapto-1,2,4-triazole (BIPMT), 4-salicylidene imino-3-propyl-5-mercapto-1,2,4-triazole(SIPMT) and 4-cinnamalidene imino-3-propyl-5-mercapto-1,2,4-triazole(CIPMT) against corrosion of mild steel in aqueous solutions of 20% formic acid and 20% acetic acid Using weight loss and potentiodynamic polarization and impedance methods were studied. Ail tested inhibitors showed good inhibition efficiency (IE). The IE was found to vary with concentiation, temperature, immersion time, and concentration of acid solution. The potentiodynamic polarization results revealed that all the compounds were mixed type inhibitors. The adsorption of these compounds on the mild steel surface exposed to both acids has been found to obey Langmuir adsorption isotherm.