Abstract: Liquid phase precipitation method,which is easy to be industrialized,was adopted to synthesize nano-sized magnesium hydroxide.Under the synergic action of mixed surface modifiers [sodium dodecyl sulfate (SDS) and sodium polyacrylate (PA-Na)],modified nano-sized magnesium hydroxide with the yield of about 98% was synthesized.Experiments proved that optimum dosage of mixed modifiers was 0.2% of the mass of magnesium hydroxide and mass ratio of SDS to PA-Na was 1∶1.Unmodified and modified samples were characterized by BET,apparent density apparatus,X-ray diffraction (XRD),transmission electron microscope (TEM) etc.respectively.Results showed that modified samples had good dispersivity and high crystallinity degree.Fourier transform infrared spectroscopy (FT-IR) and sedimentation volume experiments results indicated mixed surfactants were adsorbed onto the surface of magnesium hydroxide nanoparticles changing hydrophilic surface into lipophilic and improving dispersion stability of nano-sized magnesium hydroxide in organic media.It was discovered that SDS and PA-Na can be adsorbed onto the surface of sample in the form of monomolecular layer or bilayer.They mainly relied on steric effect of long carbon chains and electrostatic stabilizing effect generated by the dissociation of large amount of electric charges to affect agglomeration of particles,and consequently good dispersion flaky samples were obtained. 