The inhibition effect of 3-(4-((Z)-indolin-3-ylideneamino)phenylimino)indolin-2-one Schiff base (PDBI) on mild steel corrosion in 1 M HCl solution was studied by using electrochemical techniques such as potentiodynamic polarization curves, weight loss, electrochemical impedance spectroscopy, and linear polarization resistance. PDBI has remarkable inhibition efficiency on the corrosion of mild steel in 1 M HCl solution. Polarization measurements indicated that PDBI acts as mixed type corrosion inhibitor. The adsorption of PDBI on the mild steel surface obeys Langmuir adsorption isotherm. These results were supplemented by atomic force microscopy and scanning electron microscopy.