The current study was designed to give more knowledge and helping to exploit the leaves of the plants L. stoechas collected in Tlemcen region in the west of Algeria by determining the anti-corrosive activity of its essential oil. The inhibitory efficiency of the essential oil of the plant obtained by hydrodistillation and characterized by GC and GC/MS was studied using gravimetric and electrochemical methods (polarization curves and electrochemical impedance). The effect of temperature on the corrosion behavior of the steel and the inhibitory efficiency was studied in a temperature range of 303-323 K at 2 g/L. The surface morphology of the samples immersed in 1 M HCl for 24 h, before and after adding inhibitor at (2 g/L at 30 °C) was analyzed by scanning electron microscope (SEM) Quanta 250 with tungsten filament from the company FEI. Results show that the addition of the essential oil of the plant to the medium induces a diminish in the rate of corrosion and augmentation in the inhibitory efficiency of the oil. We established that the inhibition efficiency increase with concentration of the essential oil of lavender to attain 76.19% at 2 g/L. Polarization curves revealed that lavender oil react as a mixed-type inhibitor. EIS spectra exhibit one capacitive loop and confirm the inhibitive ability, and the changes in impedance parameters were indicative of adsorption of essential oil of lavender on the metal surface. The thermodynamic parameters indicate that the adsorption of the molecules of the oil takes place according to the Langmuir isotherm in the corrosive medium studied and that they are physisorbed on the metal surface. The analysis of the surface by electron microscopy demonstrates the absence of surface attack patterns in the presence of the oil. The results obtained from different tested techniques were in good agreement.