Abstract: Flame retardent magnesium hydroxide with high dispersion，high flame retardancy，and high purity was synthesized by hydrothermal process with MgCl₂·6H₂O and NaOH as raw materials，with sodium dodecyl sulfate as dispersing agent，and ethanol as crystal control agent（to improve the product′s crystallization behavior）.The particle size distribution and morphology of the prepared magnesium hydroxide were characterized by laser particle analyzer，X-ray diffraction and scanning electron microscope（SEM）.Results indicated that feeding mode，hydrothermal time，and hydrothermal temperature all had great impact on particle size and on crystal growth direction of the product.

Key words: magnesium hydroxide, flame retardant, hydrothermal reaction, particle size distribution