The inhibitive action of octadecylamine with various concentrations on mild steel in 1.0 M HCl solution was carried out by using chemical (weight loss method) and electrochemical techniques (Potentiodynamic polarization and Electrochemical Impedance Spectroscopy (EIS)). In general, the inhibition efficiency increased and corrosion rates decreased as the increasing concentrations of octadecylamine at each temperature with same immersion time period. But on the other hand the inhibition efficiency decreased and corrosion rate increased with increasing temperature at same concentration. The inhibition was assumed to occur via adsorption of the inhibitor molecule on the metal surface. Electrochemical impedance measurement shows that charge transfer resistance increased and double layer capacitance decreased with increasing inhibitor concentrations indicates the adsorption mechanism. Polarization curves reveled that octadecylamine behave as mixed type inhibitor in 1.0 M HCl solution. The adsorption of the inhibitor was well described by the Langmuir adsorption isotherm and the adsorption isotherm parameters were determined at different temperatures. The results from all techniques show that octadecylamine acts as a very good inhibitor.