The inhibition effect of N,N-diethylammonium O,O'-dicyclohexyldithiophosphate(NOCP) against the corrosion of carbon steel in HCl solution was studied by weight loss measurement, potentiodynamic polarization and atomic force microscopy techniques. The studies of weight loss measurement show that the inhibition efficiency was up to 99.54 % at the inhibitor concentration of 2.717×10-4 M in 1.0 M HCl solution at 25°C. The adsorption of NOCP on carbon steel surface obeys the Langmuir isotherm. Polarization curves indicate NOCP is a mixed-type inhibitor, and the obtained standard free energy of adsorption suggests that the chemisorption takes place spontaneously. The effects of temperature, acid concentration and immersion time were also studied.