Nickel sulfide nanocrystals with novel morphologies of two-dimensional nanosheets and one-dimensional (ID) nanoneedles or nanotubes have been successfully achieved in the CTAB/n-pentanol/n-hexane/water microemulsion under hydrothermal condition at 130degreesC. X-ray powder diffraction, transmission electron microscopy (TEM) and field emission scanning electron microscopy were used to characterize the as-synthesized samples. The result shows that nickel sulfide nanosheets with small thickness (less than 5 nm) and nanoneedles with hollow center (or nanotubes), ca. 50-150nm in diameters and several microns in lengths, can be obtained by hydrothermally treating for 5 and 15h, respectively. The sulfuration reaction mechanism and the low-dimensional nanocrystal growth process have been discussed in detail. TEM images reveal that the nanosheets firstly formed under the soft template action of the wo microemulsion, and then the resulting nanosheets rolled up into ID nanoneedles or nanotubes. The sulfuration reaction is a sequential process in which a lower sulfide initially forms and then it goes on to react with S2- to produce more sulfur-rich sulfides. (C)2003 Elsevier B.V. All rights reserved.