The effects of 1,2-diaminoethane (DE), 1,6-diaminohexane (DH), 1,8-diaminooctane (DO), and hydrazine (H) on the electrochemical behavior of copper in 0.1 M H2SO4 were investigated using the potentiodynamic polarization and electrochemical impedance spectroscopy methods at 298 K. A significant decrease in the corrosion rate of copper was observed in the presence of the investigated inhibitors. The potentiodynamic polarization data indicated that the inhibitors were of mixed type, but the cathodic effect was more pronounced. Electrochemical measurements showed that the inhibition efficiencies increased with increasing inhibitor concentration and followed the order DO > DH > H > DE. This reveals that the inhibitive actions of the inhibitors are mainly due to adsorption on the copper surface. Adsorption of these inhibitors follows a Flory-Huggins adsorption isotherm. The correlation between the inhibition efficiencies of inhibitors and their molecular structures has been investigated using quantum chemical parameters obtained by AM1 semiempirical method. Calculated quantum chemical parameters indicate that diamine compounds are adsorbed on copper surface by chemical mechanism.