[en] Cycloocteno-1,2,3-selenadiazole, an organometallic selenium precursor reacts with mercury acetate in aq. N,N'-dimethylformamide (DMF) or in ethylene glycol (EG) at a temperature between 120 and 130 deg. C to afford nano-sized HgSe. The product was characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy TEM. The electron diffraction analysis showed crystalline nature of nano-particles of HgSe. The calculation made by XRD suggest the particles size to be less than 20 nm which match well with the observations made by TEM. The current method uses 1,2,3-selenadiazole, an organo-selenium compounds thus extending the scope of organo-chalcogen compound in material science