Ammonium pyrrolidine dithiocarbamate (APDTC) is an environmentally friendly corrosion inhibitor. The anticorrosion mechanism and adsorption behavior for the self-assembled monolayers (SAMs) of APDTC on the surface of copper in 0.5 mol·L-1 HCl solution were investigated by electrochemical methods. Results indicated that APDTC was liable to interact with copper forming SAMs on the surface of copper. APDTC SAMs changed the structure of the double electric layer and restrained both the processes of anodic oxidation and cathodic reduction. Electrochemical impedance spectroscopy (EIS) measurement results indicated that the charge transfer resistance of the copper electrode with APDTC SAMs increased greatly and its double electric layer capacitance decreased significantly. This is in od agreement with the fact that APDTC SAMs have a high inhibition effect on copper in 0.5 mol·L-1 HCl solution measured by EIS and by polarization curves. Adsorption of APDTC SAMs was found to follow Langmuir's adsorption isotherm and the mechanism consisted of a mixed adsorption between chemisorption and physisorption.