High-purity nanosized magnesium hydroxide was prepared by the direct alkali hydrolysis method using hexammoniated magnesium chloride as raw material.The optimum reaction condition was obtained through experiment: the mixture of 10% sodium hydroxide and highly concentrated hexammoniated magnesium chloride reacted under a homogeneous machine for 5 h at room temperature

was deposited

filtered and washed

and then dried.The analysis of chemical composition and transmission electron microscopy (TEM) showed that the particle size was smaller than 100 nm

the content of magnesium hydroxide was about 99.7%

and the content of impurity was lower than 0.3%.