Corrosion inhibition of C-steel in 1.0 M HCl was in vestigated in the absence and presence of different concentrations of some new ionic liquids derivative s namely, 1-hexyl-3-(4-phenoxybutyl)-1H-imidazol-3- ium bromide (MS35) and 3-(4-ethoxy-4-oxobutyl)-1-hexy l-1H- imidazol-3-ium bromide (MS36) were synthesise d and their inhibitive action against the corrosion of C- steel in 1.0 M HCl solution were investigated at 30 8 K using gravimetric measurements. Results show that MS35 is a good inhibitor and inhibition efficiency reaches 97.3% at 10 -2 M. The adsorption of these compounds on C-steel su rface obeys Langmuir’s adsorption isotherm. The kin etic and thermodynamic parameters for C-steel corrosion and inhibitor adsorption, respectively, were determ ined and discussed. The comparative study of inhibitive perf ormance of the two new ionic liquids derivatives re vealed that MS35 is more effective than MS36. Quantum chemical approach, using the density functi onal theory (DFT), was applied in order to get better understanding about the relationship between the inhibition efficiency and molecular structure of MS35 and MS36.