In this paper, the biochemical constituents of Cymbopogon citratus leaf were investigated by atomic absorption spectroscopy (AAS), Fourier transform infrared spectroscopy (FT-IR) and phytochemical screening analyses for assessing its steel-rebar corrosion-protection prospects. AAS results showed that the leaf contained Fe = 4,641.025 μg/g, Mn = 849.5069 μg/g, Cu = 171.045 μg/g, Pb = 13.2938 μg/g, Ni = 11.5187 μg/g, Cd = 4.9310 μg/g, but Cr = 0.0 μg/g. FT-IR indicates the leaf-extract contained S-, N-, O-containing heteroatoms and aromatic compounds, which are rich in π-electrons and that are known to inhibit steel-rebar corrosion. Phytochemical screening results showed that Cymbopogon citratus leaf-extract contains tannins, phlobatannins, saponins, glycosides, flavonoids, steroids and terpenoids. Macrocell corrosion tests, as per ASTM G109-99a, showed that the plant reduced total corrosion in 0.5 M H2SO4-immersed steel-reinforced concrete samples. These indicated positive prospects of Cymbopogon citratus as an eco-friendly inhibitor of steel-reinforcement corrosion in concretes designed for acidic sulphate service-environment.