An advanced method has been developed to synthesis magnesium oxysulfate hydrate (5Mg(OH)(2)center dot MgSO4 center dot 3H(2)O, abbreviated as 513MOS) whiskers via co-precipitation-hydrothermal reaction route, using MgSO4 and NaOH as the reactants. Mg(OH)(2) slurry synthesized at room temperature was treated in MgSO4 hydrothermal solution. 513MOS whiskers co-existed with the sector-like whiskers were formed after hydrothermal treatment at 200 degrees C for 2.0 h. The presence of ethylenediaminetetraacetic acid (EDTA) in hydrothermal treatment inhibited the formation of the sector-like whiskers, producing 513MOS whiskers with perfect morphology (50-80 mu m in length and 0.2-0.6 mu m in diameter). Thermodynamic calculation results indicated that the addition of EDTA was favorable for the dissolution of Mg(OH)2 and the homogeneous precipitation of 513MOS owing to the complex interaction between EDTA and Mg2+. XRD analysis showed that 513MOS whiskers belonged to the orthorhombic structure (a = 15.94 angstrom, b = 3.11 angstrom, c = 13.38 angstrom) and b-axis was the predominant growth direction. (c) 2006 Springer Science + Business Media, Inc.