Inhibitive and adsorption properties of ethanol extract of Lasianthera africana for inhibition of corrosion of mild steel in H2SO4 were studied using gravimetric, thermometric, gasometric, and infrared (IR) methods. The extract was found to be a good inhibitor of corrosion of mild steel in H2SO4. Inhibitive properties of the extract were attributed to enhancement in adsorption of the inhibitor on mild-steel surface by saponin, alkaloid, tannin, flavanoid, cardiac glycoside, and anthraquinone (present in the extract). Also, adsorption of the inhibitor was found to be exothermic, spontaneous, and consistent with assumptions of Langmuir and Temkin adsorption isotherms. Synergistic study revealed that, of the investigated halides, only KCl may enhance adsorption of the inhibitor, whereas KBr and KI antagonized its adsorption. Based on the decrease in efficiency of the inhibitor with temperature, with values of activation energy and free energy of adsorption below the threshold values of -40 and 80 kJ mol(-1), respectively, a physical adsorption mechanism has been proposed for adsorption of ethanol extract of Lasianthera africana on the surface of mild steel.