Extracts from Thai Nguyen tobacco leaves were prepared by extracting dried leave powder using distilled water. After that, extracts were extracted respectively by solvents which increased polarization. The final water extract is used as corrosion inhibitor for CT38 steel in 1M HCI solution. The corrosion inhibition has been studied using electrochemical methods and microscopic observation. The obtained results showed that the corrosion inhibition efficiency increases significantly compare with using water extract of tobacco leaves which were not extracted by solvents, from approximately 64 percent to 77 percent. Thermodynamic consideration reveals that adsorption of Thai Nguyen tobaco leaves extract on mild steel surface is spontaneous and occurs according to Langmuir adsorption isotherm. Physical adsorption mechanism has been proposed for the adsorption of the inhibitor from the values of thermodynamic parameter.