Nanostructured thermoelectric Bi2Te3 powders with various morphologies were hydrothermally synthesized using different precursors and routes to give an experimental comprehension on the formation of the nanopowders. It was found that the polyhedral Bi2Te3 particles are formed by surface nucleation in a continuous nucleation process, the hexagonal Bi2Te3 thin sheets are formed in a nucleus saturation process due to the anisotropic growth of the crystals, and the mono-atom reaction model leads to irregular bent thin Bi2Te3 sheets. Some quasi one-dimensional nanorods and nanotubes were also found in the synthesized Bi2Te3 powders.