Nano-Mg(OH)(2) was synthesized with an in situ deposition technique, and its size was confirmed by X-ray diffraction. A polypropylene-Mg(OH)(2) composite was prepared by melt-extrusion processing. The addition of a small quantity of a nanofiller (up to 10 wt%) increased Young's modulus up to 433% with respect to the modulus of virgin polypropylene. The addition of up to 4 wt % Mg(OH)(2) produced the maximum increase, and a further decrease in the tensile strength was observed with an increase in the concentration of nano-Mg(OH)(2). Increases in the hardness and other properties were due to higher nucleation and the intercalation of polymer chains in the nanolayer galleries. The flame-retarding property was demonstrated by the rate of burning. The time required to burn the nanofilled composite was greater than the time required for virgin polypropylene. (C) 2004 Wiley Periodicals, Inc.