The effect of using Conocarpus extract as a green inhibitor on the corrosion behavior of mild steel in a 1M HCL environment was investigated by electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP), scanning electron microscopy (SEM), and Fourier-transform infrared spectroscopy (FTIR). The impedance test showed that the polarization resistance increased from 29 for the blank solution to 299 for the solution containing 2500 ppm of Conocarpus extract. The results of the polarization test showed that at room temperature, the corrosion current density for the blank solution decreased from 3.5E-4 to 2.6E-5for the solution containing 2500 ppm of Conocarpus extract, and the potential was shifted to negative values. The polarization test was performed at three temperatures of 25, 55, and 85. The results showed that the efficiency of 1925 ppm has decreased from 93% at room temperature to 86% at 85 ° C. Obviously, the high-temperature efficiency has not reduced significantly, which means the effectiveness of Conocarpus extract at high temperatures. FTIR test also proved that the corrosion inhibitory effect of Conocarpus extract is due to the presence of heteroatoms such as N, S, and O. The adsorption isotherm results showed that the adsorption of the extract as a single layer on the surface is consistent with the Langmuir isotherm.