A novel imidazolium–based ionic liquid, 3-(6-ethoxy-6-oxohexyl)-1-propyl-1H-imidazol-3-ium bromide (BK15), is presented as corrosion inhibitor for carbon steel in molar HCl. The gravimetric investigations revealed the high inhibition efficiency (IE%) of (BK15) with ca. 87.5% in the presence of ca. 3×10−3 M of the inhibitor. Temperature effect study showed that the (IE%) decreased with increasing temperature and that was attributed to a physical–type adsorption of the (BK15) protective layer onto the carbon steel surface. Thermodynamic parameters were calculated as follows: A = 3.641 × 1015 mg.cm-2.h-1 ; Ea = 95.594 kJ.mol-1 ; ΔHa = 92.951 kJ.mol-1 and ΔSa = 44.098 kJ.mol-1 showing the high effectiveness of (BK15) as corrosion inhibitor, the surface–reaction process of the occurring processes, the endothermic type of the metal corrosion and the induced disorder upon formation of the activation complex. The adsorption process best–fitted the Langmuir adsorption isotherm (R2 = 0.9999) and the calculated adsorption free energy (ΔGads = −36.860 kJ.mol-1) confirmed a mixed–type adsorption, predominantly physisorption of (BK15) in the present work conditions.