The effect of substituted and unsubstituted salicylaldehyde semicarbazones on corrosion of mild steel in cooling water system has been studied by using polarization technique. A retardation of the corrosion rate is observed in the inhibited cooling water system. The corrosion rate depends on the nature of the inhibitor, its concentration and the operating temperature of the system. The observed polarization data infer that these organic compounds act as mixed inhibitors for mild steel in simulated cooling water. The IR spectral data of the components of the corrosive medium indicate the formation of a complex between the inhibitor molecule and the metal. The thermodynamic parameters of adsorption obtained by using Frumkin adsorption isotherm revealed a strong interaction of these inhibitors molecules with the mild steel surface