Magnesium oxychloride (MOC,5Mg(OH)2•MgCl2•8H2O,phase 5) nanowhiskers were synthesized via a reverse microemulsion method by suing cetyltrimethyl ammonium bromide (CTAB)/n-butanol (C4H10O)/cyclohexane (C6H12)/water as soft-template. Aqueous solution of magnesium chloride (MgCl2) and MgO powder were suing as reactants. The products were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM). Results indicated that MOC nanowhiskers can be obtained when the mass ratio of MgO, magnesium chloride hexahydrate and water is 1:1:0.64. The aspect ratio of MOC nanowhisker is more than 100 with an average diameter of 50-90 nm. The influence of size of MgO particles and mass ratio of MgCl2 solution to CTAB on morphology of whiskers was investigated. The growth mechanism of the MOC nanowhisker was also supposed in this study.