The inhibition of corrosion of pure iron in 3.5% H3PO4 by some hydrazone derivatives has been investigated by weight loss and galvanostatic polarization techniques. The inhibition efficiency was increased by increasing inhibitor concentration and decreased by rise in temperature. Polarization studied revealed that these compounds behave as mixed-type inhibitors. The inhibition action of hydrazone derivatives was performed via adsorption of these compounds on iron surface following Frumkin adsorption isotherm. The corrosion behavior of iron in 3.5% H3PO4 solution in the presence of hydrazone-halide mixtures was studied. Some thermodynamic parameters were calculated and discussed. The correlation between the inhibition efficiency and quantum chemical parameters was investigated in order to elucidate the inhibition mechanism of the investigated compounds.