Magnesium hydroxide sulfate hydrate (MHSH) nanowhiskers were prepared using magnesium chloride, ammonia and magnesium sulfate as raw materials by hydrothermal synthesis without any additional template. X-ray powder diffraction (XRD). transmission electron microscopy (TEM) and thermal analysis (TG-DTA) were employed to characterize the composition and structural features of the MHSH nanowhiskers. It is shown that the thermal decomposition of nanowhiskers followed a three-step scheme. Based on DTA data, the reaction order, activation energy and pre-exponential factor for each step were calculated using a non-isothermal Kissinger method. It is also indicated from Satava method that the first step of the thermal decomposition of nanowhiskers is an A(2) nucleus formation and growth mechanism with integral form of G(a) =[-In(1 - a)(1/2). The second step is an A branching nuclei mechanism with integral form of G(a) = In[a/(1 - a)], and the final step is a P-1/2 nucleation mechanism with integral form of G(a)= a(1/2). (C) 2009 Elsevier B.V. All rights reserved.