Abstract: Stearic acid was adopted to modified magnesium hydroxide \[Mg(OH)₂\] by way of wet surface organic modification.Mixing the modified magnesium hydroxide into polystyrene (PS) to make inorganic fire-retardant PS-Mg(OH)₂ composite.Mechanism about the surface modification on Mg(OH)₂ was characterized and analyzed by XRD,FT-IR,TG-DSC,and SEM.And the composite effect and properties of PS-Mg(OH)₂ composite were investigated by the tests of SEM,oxygen index,and tensile-strength etc..Results showed that the surface modification of stearic acid was a process of chemical absorption in essence;the compatibility of  Mg(OH)₂ and PS base was improved greatly and the oxygen index (OI) of the composite has also been increased obviously;the OI reached about 25% when the dosage of Mg(OH)₂ was at 40%~60% of PS,and meanwhile the mechanical properties did not have any change. 

Key words: PS-Mg(OH)₂ composites, surface modification, oxygen index, mechanical property