Gravimetric, polarization, and electrochemical impedance spectroscopy studies were applied for investigation of anticorrosion behavior of synthesized indolines 2-((1-((3-methoxyphenylamino)methyl)-1-benzoimidazol-2-yl)methyl)isoindoline-13-dione (MBI) and 2-((1-(3-methylphenylamino)methyl)-1-benzoimidazol-2-yl) methyl) isoindoline-13-dione (PBI) on mild steel in 15% HCl medium. According to gravimetric measurement results, MBI and PBI showed enhanced corrosion protection ability at enhanced concentrations whereas corrosion protection ability suppressed at enhanced temperature. MBI and PBI behave as mixed inhibitor and obeyed Langmuir adsorption isotherm. The SEM, EDX, and AFM images of inhibited samples revealed the presence of protective inhibitor layer at the surface of inhibited sample, resulting in protection of mild steel from corrosion. Results obtained by Density Functional Theory satisfactorily correlate the results obtained by gravimetric and electrochemical measurements.