Corrosion inhibition effect of 2-(2-(2-phenyl)-3-(isonicotinamido)-4-oxothiazolidin-5-yl) acetic acid (PITA) and N-(2-phenyl-4-oxothiazolidin-3-yl)-isonicotinamide (POTI) on mild steel corrosion in 15% HCl solution was studied by using weight loss, electrochemical polarization and electrochemical impedance spectroscopy (EIS) techniques. It was found that the inhibition efficiency of both inhibitors increases with increase in concentration. The effect of temperature on the corrosion rate was investigated and some thermodynamic parameters were calculated. Polarization studies show that both studied inhibitors are of mixed type in nature. The results show that both POTI and PITA are good inhibitors, and the adsorption of each inhibitor on mild steel surface obeys Langmuir adsorption isotherm. Scanning electron microscopic (SEM), energy dispersive X-ray spectroscopic (EDX) and atomic force microscopy (AFM) studies were used to characterize the surface morphology of uninhibited and inhibited mild steel specimens. The morphological study indicated adsorption of inhibitor molecules on the surface of the mild steel. The density functional theory (DFT) was employed for theoretical calculations. The results obtained from experimental measurements and those from theoretical calculations are in good agreement.