Bi2Te3 nano-powders have been prepared via hydrothermal synthesis in closed and opened systems respectively by using Te powder and BiCl3 as the reactants and NaBH4 as the reductant. The morphology and microstructure investigations of the products show that novel quasi-one-dimensional Bi2Te3 nanotubes and nanocapsules with an average diameter of about 100nm have formed during the reactions. The nanotubes-contained powder was used as the additive of hot-pressed Bi2Te3 based alloys. Thermoelectric transport measurements show that the thermoelectric properties of the nano-composite bulk materials are remarkably increased. The maximum figure of merit ZT above 1.2 was achieved.