LaCuOS nanopowder was synthesized by a novel precipitation/reduction route using commercially available La(NO3)3·6H2O, CuSO4·5H2O and NH3·H2O as the starting materials. Detailed characterizations of the synthesized products were obtained by differential thermal analysis and thermogravimetry (DTA–TG), fourier transform infrared spectroscopy (FT-IR), X-ray diffractometry (XRD), transmission electron microscopy (TEM), and UV–vis absorption spectroscopy. The results revealed that the precursor, composed of amorphous lanthanum and copper hydroxide sulfate, could be converted into pure LaCuOS nanopowder by calcination at 800°C for 5h in flowing argon and hydrogen atmosphere (90%Ar+10%H2) resulting in quasi-spherical and agglomerated morphology with ~50nm in size. LaCuOS has been characterized to be a semiconductor with an optical band gap of 3.1eV by UV–vis absorption spectroscopy.