Nonacomposites of NiSe2was successfully synthesized by EDTAassisted hydrothe rm al method, adding NiSe2 with MX2 structure as seed. X_ray diffraction pa tterns indicate that the products are single phase FeS2(pyrite) with the average grain size of about 48nm. FeS2thin films were prepared by screen_printing method and annealed at high temperature. It has been shown that they have an increased direct bandgap. With increasing amount of seed, the absorbance edges in the ultraviolet_visible range show a red shift; the resistance goes up; Hall mobility rises and the carrier c oncentration decreases. The FeS2thin film shows an n_type semiconductor chara cteristic. The mechanism of the formation of FeS2(pyrite) nanocrystalline was discussed in terms of the growth process.