Abstract: Influence of sodium hydroxide (NaOH) on morphology of magnesium hydroxide [Mg(OH)<SUB>2</SUB>] particles in different hydrothermal environments was investigated with Mg(OH)2 prepared by lime milk-brine method as raw material. Influences of hydrothermal time,mass concentration of precursor,and filling degree of reactor on the growth of crystal were also studied.Specific surface area (BET) and morphology of product were respectively characterized by scanning electron microscope (SEM),X-ray diffractometer (XRD),and nitrogen adsorption BET analyzer.Results showed that lower mass concentration of Mg(OH)<SUB>2</SUB> solution (precursor) and 2/3 of filling degree were favorable for the growth of crystal.Obtained particles were hexagonal plates and had better dispersivity and uniform particle size and their specific surface area reduced to 8.15 m<SUP>2</SUP>/g from 33.38 m<SUP>2</SUP>/g.In addition,longer reaction time was not good for growth of crystal.