The corrosion inhibition and adsorption mechanism of Tridax procumbens Linn leaves extract on mild steel immersed in 1M HCl solution was investigated. Mass loss, corrosion rate and inhibition efficiency from gravimetric and potentiodynamic polarization measurements, atomic adsorption spectroscopy (AAS), Fourier transform infra red spectroscopy (FTIR), and scanning electron microscopy; were used for the analysis. The results show that within the selected range of concentration of the extract and corrosion test temperatures, the inhibition efficiency obtained was within the range of 81 and 96 %. The efficiency values were observed to increase with increase in the extract concentration but decreased slightly with increase in temperature. The inhibitor molecules were noted to be physically adsorbed on the mild steel surface with OH, NH, and CO groups confirmed as the active phytochemical constituents in the extract responsible for the adsorption. The adsorption process fitted perfectly with the Langmuir adsorption isotherm indicating that the extract was strongly adsorbed on the mild steel surface.