The corrosion protection efficiency of three pyridines namely 2-amino-3,5-dicarbonitrile-4-(4-methoxyphenyl)-6-(phenylthio)pyridine (ADTP I), 2-amino-3,5-dicarbonitrile-4phenyl-6-(phenylthio) pyridine (ADTP H), and 2-amino-3,5dicarbonitrile-4-(4-nitrophenyl)-6-(phenylthio) pyridine (ADTP III) was investigated by electrochemical impedance spectroscopy, potentiodynamic polarization, and weight loss techniques. The results of potentiodynamic polarization studies show that the three compounds under investigation show mixed-type inhibition behavior. Among them, ADTP I shows the highest inhibition efficiency of 97.6% at 1.22 mmol L-1. The effect of temperature and related activation parameters were worked out. To inspect the surface morphology and composition of inhibitor film on the mild steel surface, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) technique were used.