A facile direct synthesis has been done to prepare HgO nanocrystallites of different shapes. The effect of different parameters such as the presence of alkali salts or stabilizers, power of the ultrasound, time of sonicating, and the starting materials on the size, morphology and crystallinity degree of the products were studied. Scanning electron microscopy observations revealed that using of polyvinyl alcohol (PVA) or alkali salts led to different shapes of product. (C) 2009 Elsevier B.V. All rights reserved.