Aqueous extract of Thevetia peruviana leaves were investigated as corrosion inhibitor for API 5L X80 pipeline steel in 1M H2SO4 solution using electrochemical and gravimetric techniques. The results reveal that T. peruviana inhibited the X80 pipeline steel corrosion in the acid medium in a concentration dependent manner. Potentiodynamic polarization results showed T. peruviana to be a mixed type inhibitor in 1M H2SO4 environment, whereas the impedance results revealed adsorption of the inhibitor species on the steel surface. The gravimetric results reveal that the adsorption mechanism of the inhibitor on the steel surface was chemisorption. The adsorption was in accordance with Freundlich adsorption isotherm and negative standard adsorption energy (Δ𝐺o𝑎𝑑𝑠) obtained inferred that the adsorption was spontaneous and the interaction between the inhibitive molecules was found to be repulsive. Scanning electron microscopy (SEM) confirmed the formation of adsorbed film on the X80 pipeline steel surface. Results revealed that T. peruviana has potential to inhibit the correction and could possibly be used for corrosion inhibition in the acidic environment of steel.