The requirements for an alternative to toxic localized corrosion inhibitors have always been high-performance with localized corrosion inhibition, availability, ease of manufacturing, cost-effectiveness and ecological safety. Due to its reputation in South East Asian countries as a vegetable of low-cost and environmental friendliness, Aganonerion polymorphum, or rather its leaf extract, can be a source of environmentally friendly and high-performing inhibitors. The effect of water extract of Aganonerion polymorphum leaf (APLWE) on carbon steel in 0.1 M naturally-aerated HCl solution was studied as a potential corrosion inhibitor using electrochemical techniques and surface analyses. The outcome demonstrated the mixed inhibition behavior of APLWE on the steel surface in holding back the electrochemical corrosion reactions by the establishment of a highly resistive layer, resulting in a reduction of the corrosion penetration rate. Surface appraisals indicated the existence of an adsorbed film as a complex between metal ions and an organic film of APLWE components, thereby preventing a case of corrosive degradation on the steel. The details of theoretical methods are in close agreement with experimental results, which confirmed the role of APLWE as an inhibitor through adsorption activities, providing corrosion resistance for steel in a hydrochloric environment.