Abstract: Magnesium hydroxide whiskers were prepared via hydrothermal synthesis method using basic magnesium sulfate whiskers（MHSH） and sodium hydroxide as reactants.The optimal experimental conditions have been confirmed by experiment:the amount-of-substance ratio of MHSH to NaOH was 1∶2，the reaction temperature was 200 ℃，the reaction time was 3 h， mass fraction of MHSH pulp was 4%，and the concentration of sodium hydroxide was 0.3 mol/L.SEM，XRD，and TG-DTG were performed for analysis of magnesium hydroxide whiskers.The prepared whiskers with diameter of 1～2 μm，length of 100～200 μm，and aspect ratio of 100～200 were fan-like.Magnesium hydroxide whiskers were modified by surface  modification agents，such as KH-550，stearic acid，sodium dodecyl benzene sulfonate，sodium stearate，potassium oleate and so on.Results indicated that when using the potassium oleate as surface modification agent，controlling the mass fraction of magnesium hydroxide whiskers pulp at 5%，modification time at 30 min，modification temperature at 90 ℃，and potassium oleate dosage of 5%（mass fraction），a good surface modification effect can be achieved，and the activation index of the modified magnesium hydroxide whiskers reached 99.48%.

Key words: magnesium hydroxide, whiskers, hydrothermal synthesis, surface modification