Colloidal nanocrystals (quantum dots (QDs)) of mercury selenide have been synthesized and the effect of size quantization on their basic properties has been investigated. The current-voltage characteristics of single QDs (less than 10 nm) had features in the form of separate regular peaks and quasi-periodic current oscillations with voltage intervals (0.1–0.2) V. The observed features were explained in the models of size quantization and Bloch oscillations. The absorption spectra in the range up to 25 μm had eight certain peaks, including five – interband and intraband transitions and three – with energies (145–215) meV, which are explained as intraresonant. Calculations show that it is possible to have IR photosensitivity in the wavelength range up to 40 μm.