The inhibition properties of phytic acid (PA) on Q235 mild steel corrosion in 0.5 M H2SO4 was estimated using electrochemical techniques. Polarization results revealed PA to be a mixed-type inhibitor in 0.5 M H2SO4, with a more pronounced cathodic effect, while impedance results indicate adsorption of the PA species on the steel surface. The values of the synergistic factor with KI were higher than unity indicating that both additives act cooperatively to improve inhibition performance. The adsorption of PA followed the Langmuir adsorption isotherm. The mechanism of chemical adsorption is proposed on the basis of the trend of inhibition efficiency with temperature and the calculated values of the activation energy (E-a). Scanning electron microscopy, atomic force microscopy, and Fourier transform infrared spectroscopy studies revealed the formation of a protective film adsorbed on a mild steel surface. Quantum chemical calculations were used to confirm the ability of phytic acid to adsorb on a steel surface.