Abstract: Flame retardant magnesium hydroxide (Mg(OH)₂) particles were synthesized by liquid phase hydrolysis method with magnesium chloride (MgCl₂·6H₂O) and sodium hydroxide (NaOH) as raw materials,sodium dodecyl sulfate and ethanol as dispersing agents.The influences of mixing procedure,the dosage of dispersants,reaction temperature,reactant concentration and concentration ratio on particle size and absorbance were explored by orthogonal experiment.The magnesium hydroxide particles obtained under the best technological conditions were characterized by X-ray diffraction (XRD) and scanning electron mmicroscope (SEM).The best technological conditions are as following:sodium hydroxide was added to magnesium chloride and dispersant mixed solution,the dosage of dispersants 6%,reaction temperature 50℃,reactant magnesium chloride concentration 0.75 mol/L and concentration ratio of magnesium to hydroxyl 1:2.This synthetic method is featured by simplicity in process and mild operation condition.The synthesized flame retardant magnesium hydroxide particles are more uniformed and with smaller size,narrower size distribution,better polarity,dispersion and anti-aggregation performance compared to the commercially available products.