The synergistic inhibition of the corrosion of aluminum in acidic medium by polyethylene glycol (PEG) and the antibiotic ciprofloxacin was investigated. Significant increase in the inhibition of the corrosion of aluminum was observed by the addition of ciprofloxacin than by PEG alone. It was found that ciprofloxacin increase the inhibition efficiency of PEG from 61 to 91%. The addition of ciprofloxacin increases the kinetic thermodynamic parameters of the corrosion of aluminum such as the free energy of activation, the enthalpy of activation, and the entropy of activation which is consistent with observed increase in the inhibition efficiency. The higher absolute Delta G(ads)(o) indicates that the adsorption of PEG on the surface of aluminum is more spontaneous in the presence of ciprofloxacin. The scanning electron microscope (SEM) images of aluminum surface before and after the exposure to HCl reveals the mechanism of the inhibition. The SEM images show that the decrease in corrosion is due to the formation of well-ordered and smooth layer of PEG and ciprofloxacin on the surface of aluminum. Langmuir isotherm was found to fit properly the adsorption of PEG and ciprofloxacin over the aluminum surface. The observed synergy is attributed to a stronger binding of PEG to the surface of aluminum mediated by ciprofloxacin.