Corrosion inhibition of carbon steel in 1.0 M HCl was investigated in the absence and the presence of different concentrations of 1-(2-(4-chlorophenyl)-2-oxoethyl)pyridazinium bromide (CPEPB). This inhibitive action against the corrosion of carbon steel in 1.0 M HCl solution was investigated at 298 K using gravimetric and electrochemical measurements. The effect of temperature on the corrosion behavior with the addition of CPEPB in the range of temperature from 298 to 328 K. The inhibition efficiency decreases slightly with the increase in the temperature. Results show that CPEPB is a good inhibitor and inhibition efficiency reach 91% at 10- 3 M. The adsorption of this compound on carbon steel surface obeys Langmuir's adsorption isotherm. The kinetic and thermodynamic parameters were determined and discussed. Quantum chemical approach, using the density functional theory (DFT), was implemented in order to get a better understanding about the relationship between the inhibition efficiency and molecular structure of CPEPB and the calculated quantum chemical parameters were discussed. © 2015 Elsevier B.V. All rights reserved.