By using different Mg vapor sources, different diameters of MgO whiskers and sheets were obtained via different growth mechanisms. When the Mg vapor was generated by carbothermal reduction of MgO and C powder, small MgO nanowhiskers (50 nm in diameter) and nanosheets (700 nm in width and 60-80 nm in thickness) were formed via vapor liquid-solid (VLS) and vapor-solid (VS) processes. When the Mg vapor was generated by thermal evaporation of Mg powder, large MgO whiskers (0.6-2 mum in diameter) and sheets (2.4 mum in width and 1.5 mum in thickness) were formed, and the growth process was dominated by the VS mechanism. Experimental results suggested that the difference of Mg vapor concentration in the reaction tube is possibly responsible for the difference of the size and growth mechanism of the products. (C) 2002 Elsevier Science B.V. All rights reserved.