We report on a controlled synthesis of BN tubular layers-coated aluminum borate (Al18B4O33) nanowhiskers via a sol-gel and post-thermal-treatment method. A new boron source, trimethyl borate is used as a novel reactant. The Al18B4O33 nanowhiskers with diameters of similar to 20-50 nm and length of similar to 0.5-2 mu m are homogeneously sheathed over their entire lengths with thin BN tubular layers. The dependence of product morphology and structure has been investigated systematically. The pioneering studies on BN-coated Al18B4O33 nanowhiskers reinforced Mg matrix composites reveal that the protective BN coatings can effectively prevent the interfacial reaction between Al18B4O33 nanowhiskers and Mg alloys. A remarkable increase in composite hardness has been obtained by the addition of coated nanowhiskers into Mg alloys with a suitable content. The present BN-coated nanowhiskers reinforced Mg matrix composites are expected to have effective applications in aerospace community. (C) 2011 Elsevier B.V. All rights reserved.