The　tetragonal　phase　CuInS2　nanoparticles　were　synthesized　by　the　reaction　of　Cu(Ac)2,　InCl3·4H2O　and　thioacetamide　by　hydrothermal　method　at　200　°C　for　6　h　in　pH　1.　The　products　were　characterized　by　X-ray　diffraction,　energy-dispersive　X-ray　spectrum,　X-ray　photoelectron　spectroscopy,　scanning　electron　microscopy　(SEM)　and　transmission　electron　microscopy　(TEM)　techniques.　Experimental　results　indicate　that　reaction　temperature　and　the　pH　of　solution　are　the　important　factors　in　the　formation　of　CuInS2.　The　SEM　and　TEM　results　illuminated　that　the　CuInS2　was　composed　of　so　many　nanoparticles.　©　(2012)　Trans　Tech　Publications,　Switzerland.