The inhibition of the corrosion of carbon steel in 1 M H3PO4 solutions by some benzothiazole derivatives has been investigated using weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and electrochemical frequency modulation (EFM) techniques. Inhibition was found to increase with increasing concentration of the benzothiazole derivatives but decreased with rise in temperature. The inhibition was assumed to occur via adsorption of the inhibitor molecules on the metal surface. The adsorption of these compounds on carbon steel surface obeys the Temkin's adsorption isotherm. Potentiodynamic polarization measurements showed that benzothiazole derivatives act as mixed-type inhibitors.