The inhibitive effect of polyacrylamide grafted with fenugreek mucilage, a natural grade polysaccharide, on the corrosion of mild steel in 0.5M H2SO4 has been investigated by weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy. An inhibition efficiency of 78% has been obtained at a concentration as low as 1 ppm and efficiency as high as 96% at 100 ppm. The polarization studies reveal that it acts as a predominantly cathodic inhibitor. The adsorption of this inhibitor on the mild steel surface obeys a Langmuir adsorption isotherm. The deposited films on the electrode surface have been analyzed by using microscopic techniques. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 116: 810-816, 2010