The inhibition effect of 4-hydroxyquinoline-2-carboxylic acid was tested against mild steel in 1M H2SO4 solution by weight loss method, Electrochemical Impedance Spectroscopy (EIS) and Tafel polarization studies. From these studies the concentration of the inhibitor increases, inhibition action also increases. The inhibitor showed 87 % of inhibition efficiency at the optimum concentration of 300 ppm in weight loss method. The increase of inhibiting effect is also proved by EIS studies, because it shows 89 % of inhibition efficiency. A Tafel polarization curve indicates the used inhibitor is a mixed-type. Inhibitor is adsorbed on the mild steel surface followed by Langmuir adsorption isotherm. Surface morphology of the mild steel was analyzed using Scanning Electron Microscope (SEM) and Atomic Force Microscope (AFM) studies.