The synthesis of colloidal quantum dots of mercury selenide using mercury oxide as a precursor is proposed. The proposed method is characterized by the use of a less toxic component in the reaction mixture - mercury oxide. The transmission electron microscopy method established an average diameter of 5–6 nm and the shape of quantum dots. A histogram of the size distribution of synthesized nanoparticles is presented. An important property of the synthesized nanoparticles is the crystal structure established by X-ray diff raction analysis. The established properties of the synthesized nanocrystals coincide with the literature data. The elemental composition of the nanoparticles was controlled by X-ray microanalysis. It is established that the chemical composition of quantum dots corresponds to the stoichiometric ratio of Hg elements : Se = 0,98 : 1,00. In addition, it follows from the X-ray that the oxygen content has been identifi ed in silicon and carbon compounds, HgSe-based quantum dots do not contain traces of oxidation. The optical properties of quantum dots depend on the size of the nanoparticles. If the average diameter does not exceed 10 nm, mercury selenide particles are characterized by a monocrystalline structure with intraband absorption, the spectral energy distribution of which is subjected to dimensional quantization. As can be seen from the absorption spectra, the synthesized nanoparticles are characterized by absorption bands in the IR region, in the wavelength range up to 40 microns. The synthesized quantum dots do not possess luminescent properties, which, according to the literature data, is associated with a low probability of exciton formation for small nanoparticles (5–6 nm).