Corrosion inhibitors are substances that are coated on the metal surface so as to avoid direct contact of the metal with the surrounding. Many natural products have inhibitory properties due to the presence of heterocyclic constituents such as alkaloids, flavonoids. Presence of tannins, cellulose and polycyclic compounds aids in formation of a protective film over the metal surface. In this article the inhibitory actions of Nerium oleander leaf extract as corrosion inhibitor for mild steel in 3.5% NaCl was investigated by weight loss method and electrochemical studies. Weight loss study reveals that N. oleander is a potential inhibitor in 3.5% NaCl. Satisfactory Inhibition Efficiencies (IE) were observed. It was also seen that the IE increases with increase in temperature, indicating chemisorptions of the inhibitor on metal surface. Linear polarisation studies coincided with the weight loss study. Potentiodynamic polarisation study reveals the inhibitor as the mixed type of inhibitor. The formation of the protective film on the metal surface was confirmed by Fourier Transform Infra-Red (FTIR) spectroscopy. Surface morphology was studied by Scanning Electron Microscopy (SEM).