The inhibiting effect of streptoquin and septazole towards the corrosion of the copper in 0.1M of HCl solution has been studied by potentiodynamic polarization measurements, electrochemical impedance spectroscopy (EIS) and Electrochemical frequency modulation technique (EFM). Potentiodynamic polarization curves indicted that these compounds behave as mixed-type inhibitors. These drugs were adsorbed on copper surface follow Langmuir adsorption isotherm. The results obtained from EIS and EFM are in good agreement with potentiodynamic polarization measurements. Some quantum chemical parameters were calculated and compared with the experimental data.