Self-assembled monolayers (SAMs) of arginine (Arg) were formed on copper surface. The corrosion protection properties of the Arg SAMs were examined by electrochemical impedance spectroscopy and polarization techniques in 0.5 M HCl solution. The results show that Arg SAMs have limited protection effect. The protective efficiency increased with an increase of self-assembly time and reached maximum protection at 6 h. When iodide ion was added to the Arg-containing solution, the ability of the corrosion inhibition of the mixed SAMs improved significantly. The corrosion protection mechanism of Arg SAMs is discussed based on AM1 quantum-chemical calculations.