A new route to ternary tin selenide in mild conditions has been uncovered in this paper. Nanocrystalline Cu2SnSe4 was directly synthesized from the reaction of CuCl2.2H(2)O, SnCl2.2H(2)O(2) and elemental selenium through solvothermal process in ethylenediamine at 140 degrees C for 15 h. X-Ray powder diffraction (XRD) pattern and transmission electron microscope (TEM) images indicate that the product is a pure cubic Cu2SnSe4 phase in the form of well crystallization with an average grain size of ca. 15 nm. The mechanism of the formation of the Cu2SnSe4 nanocrystals in the solvothermal process is proposed. The solvent ethylenediamine plays an important role in the growth of nanocrystals.