The purpose of this paper is to evaluate the inhibitive action of an ethanol extract from the leaves of Pachycormus discolor (EEPD) on the corrosion of carbon steel in 1 M HCl at different temperatures; gravimetric method and electrochemical tests were conducted. Potentiodynamic polarization was used at room temperature and resistance polarization at different temperatures. Thermodynamic adsorption parameters are shown in order to demonstrate the spontaneous adsorption. The inhibition of EEPD was performed via adsorption of the extract species on the carbon steel surface. The ethanol extract obeys Langmuir adsorption isotherm. Potentiodynamic polarization results indicate that the ethanol extract acts as a mixed type inhibitor. The results revealed that the inhibition efficiency (IE) of EEPD increases (when the concentration is increased). Phytochemical and FTIR analyses are also presented in this work. It was found that the IE increases with the temperature in a 2.0% v/v solution which showed 94.52% IE at 2 5 ∘ C and 97.89% at 7 5 ∘ C.