The surface-treatment of self-assembled monolayer(SAMs）of stearic acid on pure magnesium is studied to improve the bioactivity and corrosion resistance of pure Mg. Three pre-treatment methods(HCl-NaOH treatment, alkali-heat treatment and heat treatment）are used before SAMs treatment is carried out in stearic acid. The orthogonal test is performed to select the best pre-treatment method, concentration of solution and soaking time. The electrochemical properties of samples with different pre-treatment are tested. The water contact angles of samples with and without SAMs treatment are studied. Samples are also immersed in simulated body fluid(SBF), the pH varieties of the solution and the concentration of Mg ion in SBF is tested to evaluate the corrosion resistance of SAMs, and surface morphology and composition analysis of samples are characterized by the scanning electron microscope with energy dispersive spectrometer(SEM-EDS). The results show that the sample with heat pre-treatment soaked into 0.5 mol/L stearic acid/ethanol solution for 1.5 hours has the best corrosion resistance. SAMs change the hydrophilic nature of samples and the contact angle with water significantly increases. Also SAMs decrease the corrosion rate of magnesium and samples with SAMs show better bioactivity than untreated magnesium.