A 100-nm CuFeS2 ultrafine powder was prepared through a solvothermal reaction at 200–250 °C. X-ray powder diffraction and transmission electron microscopy results revealed that chalcopyrite-phase CuFeS2 was crystallized with single-crystalline nature and preferential orientation growth. Mössbauer spectrum exhibited a six-peak hyperfine magnetic spectrum and a single nonmagnetic peak. Elemental analysis gave the atomic ratio of Cu:Fe:S of 1:1.02:2.10. The influence factors on the formation of CuFeS2 ultrafine powder are discussed.