The corrosion-of mild steel in simulated seawater containing various concentrations of hydrazine, phenylhydrazine and 2, 4-dinitrophenylhydrazine has been studied by polarization technique. These compounds inhibit corrosion effectively even in trace concentration. The degree of corrosion inhibition is a function of temperature, concentration and nature of the inhibitor. The corrosion current density, percentage inhibitor efficiency and thermodynamic parameters for the surface adsorption of inhibitors were calculated for the inhibition process. The IR spectra of the film formed on the corroding surface indicated the formation of complex between the inhibitor molecule and the mild steel. The inhibitors appeared to function through a general adsorption mode following the Frumkin adsorption isotherm. The thermodynamic parameters of adsorption showed a strong interaction of these inhibitor molecules with the mild steel surface. The results revealed that these compounds act as mixed inhibitors for mild steel in simulated seawater.