The inhibitive effects of some antibacterial cephalosporin (cefotaxime, cefalexin, cefradine and cefazolin) on the corrosion of iron in 0.5 M H2SO4 solution was investigated using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. Results showed that the inhibition efficiency increased with an increase in concentration of inhibitor. Potentiodynamic studies proved that the inhibitors act as mixed type .The inhibitors are adsorbed on the iron surface according to Langmuir isotherm equation. All impedance spectra in EIS tests exhibit one capacitive loop which indicates that the corrosion reaction is controlled by charge transfer process. Inhibition efficiencies obtained from Tafel polarization, charge transfer resistance (Rct) is consistent.