Grapheme/ whiskery magnesium hydroxide sulfate composite powders were prepared by hydrothermal synthesis method with anhydrous magnesium sulfate, ammonia and graphite oxide as raw material, and sodium dodecy benzene sulfonic acid as surface active agent in this paper. The effect of hydrothermal synthesis temperature and holding time on the preparation of grapheme/ whiskery magnesium hydroxide sulfate composite powders were discussed. The phase composition, microstructure of the products were investigated by powder X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). It indicated that: 1) The magnesium hydroxide sulfate whisker can be synthesized under the hydrothermal temperature of 190℃. 2) Increasing holding time was beneficial to the growth of whisker, there are only few of whiskers formed at holding time of 9h, however, the quantity of the whisker evidently increases as the holding time increases to 12h and 15h.