New organic ammonium salts, namely: 4-oxo-4-(2-(pyridin-4-yl)hydrazineyl)but-2-enoate tetraethyl ammonium, B1, 2-(2-(pyridin-4-yl)hydrazine-1-carbonyl)benzoate tetraethyl ammonium, B2, 4-oxo-4-(2-(pyridin-4-yl)hydrazineyl)butanoate tetraethyl ammonium, B3, 5-oxo-5-(2-(pyridin-4-yl)hydrazineyl)pentanoate tetraethyl ammonium, B4, were successfully synthesized and confirmed structures by spectral techniques. The new organic ammonium salts were used for mild steel as a protective corrosion inhibitor. Organic salts were tested with 3.5% saline solution for 24 hours at room temperature and carried out with the method of weight loss. The inhibition efficiency results for organic inhibitors (B1-B4) were increased with increasing the concentrations of organic ammonium salts and that also accompanied with the corrosion rate to be decreased. By increasing the inhibition efficiency, the coverage surface degree factor was increased. The values of thermodynamic parameter (free energy) were predicted the physisorption effect with all organic ammonium salts (B1-B4).